forked from Minki/linux
KVM: MMU: fix detecting misaligned accessed
Sometimes, we only modify the last one byte of a pte to update status bit, for example, clear_bit is used to clear r/w bit in linux kernel and 'andb' instruction is used in this function, in this case, kvm_mmu_pte_write will treat it as misaligned access, and the shadow page table is zapped Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com> Signed-off-by: Avi Kivity <avi@redhat.com>
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@ -3602,6 +3602,14 @@ static bool detect_write_misaligned(struct kvm_mmu_page *sp, gpa_t gpa,
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offset = offset_in_page(gpa);
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pte_size = sp->role.cr4_pae ? 8 : 4;
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/*
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* Sometimes, the OS only writes the last one bytes to update status
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* bits, for example, in linux, andb instruction is used in clear_bit().
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*/
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if (!(offset & (pte_size - 1)) && bytes == 1)
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return false;
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misaligned = (offset ^ (offset + bytes - 1)) & ~(pte_size - 1);
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misaligned |= bytes < 4;
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