s390x/mmu: Better storage key reference and change bit handling
Any access sets the reference bit. In case we have a read-fault, we should not allow writes to the TLB entry if the change bit was not already set. This is a preparation for proper storage-key reference/change bit handling in TCG and a fix for KVM whereby read accesses would set the change bit (old KVM versions without the ioctl to carry out the translation). Reviewed-by: Cornelia Huck <cohuck@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Message-Id: <20190816084708.602-6-david@redhat.com> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
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@ -421,13 +421,27 @@ nodat:
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return 0;
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}
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if (*flags & PAGE_READ) {
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key |= SK_R;
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switch (rw) {
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case MMU_DATA_LOAD:
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case MMU_INST_FETCH:
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/*
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* The TLB entry has to remain write-protected on read-faults if
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* the storage key does not indicate a change already. Otherwise
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* we might miss setting the change bit on write accesses.
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*/
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if (!(key & SK_C)) {
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*flags &= ~PAGE_WRITE;
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}
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break;
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case MMU_DATA_STORE:
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key |= SK_C;
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break;
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default:
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g_assert_not_reached();
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}
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if (*flags & PAGE_WRITE) {
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key |= SK_C;
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}
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/* Any store/fetch sets the reference bit */
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key |= SK_R;
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r = skeyclass->set_skeys(ss, *raddr / TARGET_PAGE_SIZE, 1, &key);
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if (r) {
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