When using a memory-backend object with prealloc turned on, QEMU
will memset() the first byte in every memory page to zero. While
this might have been acceptable for memory backends associated
with RAM, this corrupts application data for NVDIMMs.
Instead of setting every page to zero, read the current byte
value and then just write that same value back, so we are not
corrupting the original data. Directly write the value instead
of memset()ing it, since there's no benefit to memset for a
single byte write.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Message-id: 20170303113255.28262-1-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Original problem description by Greg Kurz:
> Since commit "9a4c0e220d8a hw/virtio-pci: fix virtio
> behaviour", passing -device virtio-blk-pci.disable-modern=off
> has no effect on 2.6 machine types because the internal
> virtio-pci.disable-modern=on compat property always prevail.
The same bug also affects other abstract type names mentioned on
compat_props by machine-types: apic-common, i386-cpu, pci-device,
powerpc64-cpu, s390-skeys, spapr-pci-host-bridge, usb-device,
virtio-pci, x86_64-cpu.
The right fix for this problem is to make sure compat_props and
-global options are always applied in the order they are
registered, instead of reordering them based on the type
hierarchy. But changing the ordering rules of -global is risky
and might break existing configurations, so we shouldn't do that
on a stable branch.
This is a temporary hack that will work around the bug when
registering compat_props properties: if we find an abstract class
on compat_props, register properties for all its non-abstract
subtypes instead. This will make sure -global won't be overridden
by compat_props, while keeping the existing ordering rules on
-global options.
Note that there's one case that won't be fixed by this hack:
"-global spapr-pci-vfio-host-bridge.<option>=<value>" won't be
able to override compat_props, because spapr-pci-host-bridge is
not an abstract class.
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <1481575745-26120-1-git-send-email-ehabkost@redhat.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Tested-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Commit 4881658a4b introduced a call to arm_get_cpu_by_id(),
and Coverity noticed that we weren't checking that it didn't
return NULL (CID 1371652).
Normally this won't happen (because all 4 CPUs are expected
to exist), but it's possible the user requested fewer CPUs
on the command line. Handle this possibility by silently
doing nothing, which is the same behaviour as before commit
4881658a4b and also how we handle the other CPU operations
(since we ignore the INVALID_PARAM returns from arm_set_cpu_on()
and friends).
There is a slight behavioural difference to the pre-4881658a4b
situation: the "reset this core" bit will remain set rather
than not being permitted to be set. The imx6 datasheet is
unclear about the behaviour in this odd corner case, so we
opt for the simpler code rather than complicated logic to
maintain identical behaviour.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1488542374-1256-1-git-send-email-peter.maydell@linaro.org
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Add the ability for the user to use .toast files with QEMU. This format works
just like ISO files.
Signed-off-by: John Arbuckle <programmingkidx@gmail.com>
Message-id: 0C9DA454-E3DC-4291-806E-9A96557DE833@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
The address of memory regions might overflow when something wrong
happened, like reported in:
https://lists.gnu.org/archive/html/qemu-devel/2017-03/msg02043.html
For easier debugging, let's try to detect it.
Reported-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <1489496187-624-1-git-send-email-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
icount has become much slower after tcg_cpu_exec has stopped
using the BQL. There is also a latent bug that is masked by
the slowness.
The slowness happens because every occurrence of a QEMU_CLOCK_VIRTUAL
timer now has to wake up the I/O thread and wait for it. The rendez-vous
is mediated by the BQL QemuMutex:
- handle_icount_deadline wakes up the I/O thread with BQL taken
- the I/O thread wakes up and waits on the BQL
- the VCPU thread releases the BQL a little later
- the I/O thread raises an interrupt, which calls qemu_cpu_kick
- the VCPU thread notices the interrupt, takes the BQL to
process it and waits on it
All this back and forth is extremely expensive, causing a 6 to 8-fold
slowdown when icount is turned on.
One may think that the issue is that the VCPU thread is too dependent
on the BQL, but then the latent bug comes in. I first tried removing
the BQL completely from the x86 cpu_exec, only to see everything break.
The only way to fix it (and make everything slow again) was to add a dummy
BQL lock/unlock pair.
This is because in -icount mode you really have to process the events
before the CPU restarts executing the next instruction. Therefore, this
series moves the processing of QEMU_CLOCK_VIRTUAL timers straight in
the vCPU thread when running in icount mode.
The required changes include:
- make the timer notification callback wake up TCG's single vCPU thread
when run from another thread. By using async_run_on_cpu, the callback
can override all_cpu_threads_idle() when the CPU is halted.
- move handle_icount_deadline after qemu_tcg_wait_io_event, so that
the timer notification callback is invoked after the dummy work item
wakes up the vCPU thread
- make handle_icount_deadline run the timers instead of just waking the
I/O thread.
- stop processing the timers in the main loop
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This optimization is not necessary anymore, because the vCPU now drops
the I/O thread lock even with TCG. Drop it to simplify the code and
avoid the "I/O thread spun for 1000 iterations" warning.
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
There is no change for now, because the callback just invokes
qemu_notify_event.
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This dependency is the wrong way, and we will need util/qemu-timer.h from
sysemu/cpus.h in the next patch.
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
If the first timer is exactly at the current value of the clock, the
deadline is met and the timer should fire. This fixes itself on the next
iteration of the loop without icount; with icount, however, execution
of instructions will stop exactly at the deadline and won't proceed.
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
When fetching request, it should read sizeof(*hdr), not the
pointer hdr.
Signed-off-by: Li Qiang <liqiang6-s@360.cn>
Message-Id: <1489488980-130668-1-git-send-email-liqiang6-s@360.cn>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Suramya Shah <shah.suramya@gmail.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170310163948.7567-1-shah.suramya@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Most machines don't allow sysbus devices like "kvmclock" to be
created from the command-line, but some of them do (the ones with
has_dynamic_sysbus=true). In those cases, it's possible to
manually create a kvmclock device without KVM being enabled,
making QEMU crash:
$ qemu-system-x86_64 -machine q35,accel=tcg -device kvmclock
Segmentation fault (core dumped)
This changes kvmclock's realize method to return an error if KVM
is disabled, to ensure it won't crash QEMU.
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170309185046.17555-1-ehabkost@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
When a KVM_{GET,SET}_MSRS ioctl() fails, it is difficult to find
out which MSR caused the problem. Print an error message for
debugging, before we trigger the (ret == cpu->kvm_msr_buf->nmsrs)
assert.
Suggested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170309194634.28457-1-ehabkost@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
I sometimes got "Cannot access memory" when using the x command
on the monitor. Turns out that the cpu env did contain stale data
(e.g. wrong control register content for page table origin).
We must synchronize the state of the CPU before walking the page
tables. A similar issues happens for a remote gdb, so lets
do the cpu_synchronize_state in cpu_memory_rw_debug.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <1488896348-13560-1-git-send-email-borntraeger@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Using "-mem-prealloc" option for a large guest leads to higher guest
start-up and migration time. This is because with "-mem-prealloc" option
qemu tries to map every guest page (create address translations), and
make sure the pages are available during runtime. virsh/libvirt by
default, seems to use "-mem-prealloc" option in case the guest is
configured to use huge pages. The patch tries to map all guest pages
simultaneously by spawning multiple threads. Currently limiting the
change to QEMU library functions on POSIX compliant host only, as we are
not sure if the problem exists on win32. Below are some stats with
"-mem-prealloc" option for guest configured to use huge pages.
------------------------------------------------------------------------
Idle Guest | Start-up time | Migration time
------------------------------------------------------------------------
Guest stats with 2M HugePage usage - single threaded (existing code)
------------------------------------------------------------------------
64 Core - 4TB | 54m11.796s | 75m43.843s
64 Core - 1TB | 8m56.576s | 14m29.049s
64 Core - 256GB | 2m11.245s | 3m26.598s
------------------------------------------------------------------------
Guest stats with 2M HugePage usage - map guest pages using 8 threads
------------------------------------------------------------------------
64 Core - 4TB | 5m1.027s | 34m10.565s
64 Core - 1TB | 1m10.366s | 8m28.188s
64 Core - 256GB | 0m19.040s | 2m10.148s
-----------------------------------------------------------------------
Guest stats with 2M HugePage usage - map guest pages using 16 threads
-----------------------------------------------------------------------
64 Core - 4TB | 1m58.970s | 31m43.400s
64 Core - 1TB | 0m39.885s | 7m55.289s
64 Core - 256GB | 0m11.960s | 2m0.135s
-----------------------------------------------------------------------
Changed in v2:
- modify number of memset threads spawned to min(smp_cpus, 16).
- removed 64GB memory restriction for spawning memset threads.
Changed in v3:
- limit number of threads spawned based on
min(sysconf(_SC_NPROCESSORS_ONLN), 16, smp_cpus)
- implement memset thread specific siglongjmp in SIGBUS signal_handler.
Changed in v4
- remove sigsetjmp/siglongjmp and SIGBUS unblock/block for main thread
as main thread no longer touches any pages.
- simplify code my returning memset_thread_failed status from
touch_all_pages.
Signed-off-by: Jitendra Kolhe <jitendra.kolhe@hpe.com>
Message-Id: <1487907103-32350-1-git-send-email-jitendra.kolhe@hpe.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Occasionally the users try to mix the bootindex properties with the
"-boot order" parameter - and this likely does not give the expected
results. So let's add a proper statement that these two concepts
should not be used together.
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1488303601-23741-1-git-send-email-thuth@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The 'name' parameter to memory_region_init_* had been marked as debug
only, however vmstate_region_ram uses it as a parameter to
qemu_ram_set_idstr to set RAMBlock names and these form part of the
migration stream.
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20170309152708.30635-1-dgilbert@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The power state spec section 5.1.5 AFFINITY_INFO defines the
affinity info return values as
0 ON
1 OFF
2 ON_PENDING
I grepped QEMU for power_state to ensure that no assumptions
of OFF=0 were being made.
Signed-off-by: Andrew Jones <drjones@redhat.com>
Message-id: 20170303123232.4967-1-drjones@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
In armv8, this register implements more than a single bit, with
fine-grained enables for read access to event counters, cycles
counters, and write access to the software increment. This change
implements those checks using custom access functions for the relevant
registers.
Signed-off-by: Andrew Baumann <Andrew.Baumann@microsoft.com>
Message-id: 20170228215801.10472-2-Andrew.Baumann@microsoft.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: move a couple of access functions to be only compiled
ifndef CONFIG_USER_ONLY to avoid compiler warnings]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Version: GnuPG v1
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Merge remote-tracking branch 'remotes/jasowang/tags/net-pull-request' into staging
# gpg: Signature made Tue 14 Mar 2017 07:55:01 GMT
# gpg: using RSA key 0xEF04965B398D6211
# gpg: Good signature from "Jason Wang (Jason Wang on RedHat) <jasowang@redhat.com>"
# gpg: WARNING: This key is not certified with sufficiently trusted signatures!
# gpg: It is not certain that the signature belongs to the owner.
# Primary key fingerprint: 215D 46F4 8246 689E C77F 3562 EF04 965B 398D 6211
* remotes/jasowang/tags/net-pull-request:
hw/net: implement MIB counters in mcf_fec driver
COLO-compare: Fix trace_event print bug
e1000e: correctly tear down MSI-X memory regions
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This set has a handful og bugfixes to go into qemu-2.9. This includes
an update to the dtc/libfdt submodule which will fix the build errors
seen on some distributions.
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Merge remote-tracking branch 'remotes/dgibson/tags/ppc-for-2.9-20170314' into staging
ppc patch queue for 2017-03-14
This set has a handful og bugfixes to go into qemu-2.9. This includes
an update to the dtc/libfdt submodule which will fix the build errors
seen on some distributions.
# gpg: Signature made Tue 14 Mar 2017 04:00:41 GMT
# gpg: using RSA key 0x6C38CACA20D9B392
# gpg: Good signature from "David Gibson <david@gibson.dropbear.id.au>"
# gpg: aka "David Gibson (Red Hat) <dgibson@redhat.com>"
# gpg: aka "David Gibson (ozlabs.org) <dgibson@ozlabs.org>"
# gpg: aka "David Gibson (kernel.org) <dwg@kernel.org>"
# Primary key fingerprint: 75F4 6586 AE61 A66C C44E 87DC 6C38 CACA 20D9 B392
* remotes/dgibson/tags/ppc-for-2.9-20170314:
dtc: Update submodule to avoid build errors
pseries: Don't expose PCIe extended config space on older machine types
target/ppc: fix cpu_ov setting for 32-bit
target/ppc: Fix wrong number of UAMR register
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
The definition of the major() and minor() macros are moving within glibc to
<sys/sysmacros.h>. Include this header when it is available to avoid the
following sorts of build-stopping messages:
qga/commands-posix.c: In function ‘dev_major_minor’:
qga/commands-posix.c:656:13: error: In the GNU C Library, "major" is defined
by <sys/sysmacros.h>. For historical compatibility, it is
currently defined by <sys/types.h> as well, but we plan to
remove this soon. To use "major", include <sys/sysmacros.h>
directly. If you did not intend to use a system-defined macro
"major", you should undefine it after including <sys/types.h>. [-Werror]
*devmajor = major(st.st_rdev);
^~~~~~~~~~~~~~~~~~~~~~~~~~
qga/commands-posix.c:657:13: error: In the GNU C Library, "minor" is defined
by <sys/sysmacros.h>. For historical compatibility, it is
currently defined by <sys/types.h> as well, but we plan to
remove this soon. To use "minor", include <sys/sysmacros.h>
directly. If you did not intend to use a system-defined macro
"minor", you should undefine it after including <sys/types.h>. [-Werror]
*devminor = minor(st.st_rdev);
^~~~~~~~~~~~~~~~~~~~~~~~~~
The additional include allows the build to complete on Fedora 26 (Rawhide)
with glibc version 2.24.90.
Signed-off-by: Christopher Covington <cov@codeaurora.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
The FEC ethernet hardware module used on ColdFire SoC parts contains a
block of RAM used to maintain hardware counters. This block is accessible
via the usual FEC register address space. There is currently no support
for this in the QEMU mcf_fec driver.
Add support for storing a MIB RAM block, and provide register level
access to it. Also implement a basic set of stats collection functions
to populate MIB data fields.
This support tested running a Linux target and using the net-tools
"ethtool -S" option. As of linux-4.9 the kernels FEC driver makes
accesses to the MIB counters during its initialization (which it never
did before), and so this version of Linux will now fail with the QEMU
error:
qemu: hardware error: mcf_fec_read: Bad address 0x200
This MIB counter support fixes this problem.
Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Because of inet_ntoa() return a statically allocated buffer,
subsequent calls will overwrite, So we fix this bug.
Signed-off-by: Zhang Chen <zhangchen.fnst@cn.fujitsu.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
MSI-X has been disabled by the time the e1000e device is unrealized, hence
msix_uninit is never called. This causes the object to be leaked, which
shows up as a RAMBlock with empty name when attempting migration.
Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Tested-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
The currently included version of the dtc/libfdt submodule has some build
errors on certain distributions (including RHEL7). This is due to some
poorly named macros in libfdt.h; they're designed for use with the sparse
static checker, but use reserved names which conflict with some symbols in
the standard headers.
That's been corrected in upstream dtc, this updates the qemu submodule to
bring the fix to qemu.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
bb9986452 "spapr_pci: Advertise access to PCIe extended config space"
allowed guests to access the extended config space of PCI Express devices
via the PAPR interfaces, even though the paravirtualized bus mostly acts
like plain PCI.
However, that patch enabled access unconditionally, including for existing
machine types, which is an unwise change in behaviour. This patch limits
the change to pseries-2.9 (and later) machine types.
Suggested-by: Andrea Bolognani <abologna@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
A bug was introduced in following commit:
dc0ad84 target/ppc: update overflow flags for add/sub
As for 32-bit ppc target extracting bit 63 for overflow is not correct.
Made it dependent on TARGET_LOG_BITS. This had broken booting MacOS
9.2.1 image
Reported-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
The SPR UAMR has the number 13, and not 12. (Fortunately it seems like
Linux is not using this register yet - only the privileged version with
number 29 ... that's why nobody noticed this problem yet)
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
We want query-block to return the right filename, even if a commit job
put a bdrv_commit_top on top of the actual image format driver. Let
bdrv_commit_top.bdrv_refresh_filename get the filename from its backing
file.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
We want query-block to return the right filename, even if a mirror job
put a bdrv_mirror_top on top of the actual image format driver. Let
bdrv_mirror_top.bdrv_refresh_filename get the filename from its backing
file.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
In bdrv_open_inherit(), the filename is refreshed after opening the
backing file, but we neglected to do the same when the backing file
changes later.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
In some cases, bdrv_co_get_block_status() is called recursively for the
whole backing chain. The automatically inserted bdrv_commit_top filter
driver must not stop the recursion, so implement a callback that simply
forwards the request to bs->backing.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
This fixes bdrv_co_get_block_status() for the bdrv_mirror_top block
driver, which must fall through to bs->backing instead of bs->file.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
All callers pass false now, so the parameter can go away again.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Migration is the only code left in the tree that does not react
to bdrv_is_allocated() failures. But as there is no useful way
to react to the failure, and we are merely skipping unallocated
sectors on success, just document that our choice of handling
is intended.
Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
If bdrv_is_allocated() fails, we should react to that failure.
For 2 of the 3 callers, reporting the error was easy. But in
cluster_was_modified() and its lone caller
get_cluster_count_for_direntry(), it's rather invasive to update
the logic to pass the error back; so there, I went with merely
documenting the issue by changing the return type to bool (in
all likelihood, treating the cluster as modified will then
trigger a read which will also fail, and eventually get to an
error - but given the appalling number of abort() calls in this
code, I'm not making it any worse).
Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
If bdrv_is_allocated() fails, we should immediately do the backup
error action, rather than attempting backup_do_cow() (although
that will likely fail too).
Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
The driver has failed to build since commit da34e65, in qemu 2.6,
due to a missing include of qapi/error.h for error_setg().
Since no one has complained in three releases, it is easier to
remove the dead code than to keep it around, especially since it
is not being built by default and therefore prone to bitrot.
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
BlockLimits.max_transfer can be too high without this fix, guest will
encounter I/O error or even get paused with werror=stop or rerror=stop. The
cause is explained below.
Linux has a separate limit, /sys/block/.../queue/max_segments, which in
the worst case can be more restrictive than the BLKSECTGET which we
already consider (note that they are two different things). So, the
failure scenario before this patch is:
1) host device has max_sectors_kb = 4096 and max_segments = 64;
2) guest learns max_sectors_kb limit from QEMU, but doesn't know
max_segments;
3) guest issues e.g. a 512KB request thinking it's okay, but actually
it's not, because it will be passed through to host device as an
SG_IO req that has niov > 64;
4) host kernel doesn't like the segmenting of the request, and returns
-EINVAL;
This patch checks the max_segments sysfs entry for the host device and
calculates a "conservative" bytes limit using the page size, which is
then merged into the existing max_transfer limit. Guest will discover
this from the usual virtual block device interfaces. (In the case of
scsi-generic, it will be done in the INQUIRY reply interception in
device model.)
The other possibility is to actually propagate it as a separate limit,
but it's not better. On the one hand, there is a big complication: the
limit is per-LUN in QEMU PoV (because we can attach LUNs from different
host HBAs to the same virtio-scsi bus), but the channel to communicate
it in a per-LUN manner is missing down the stack; on the other hand,
two limits versus one doesn't change much about the valid size of I/O
(because guest has no control over host segmenting).
Also, the idea to fall back to bounce buffering in QEMU, upon -EINVAL,
was explored. Unfortunately there is no neat way to ensure the bounce
buffer is less segmented (in terms of DMA addr) than the guest buffer.
Practically, this bug is not very common. It is only reported on a
Emulex (lpfc), so it's okay to get it fixed in the easier way.
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>