Re: [PATCH 10/11] KVM: MMU: fix detecting misaligned accessed

Avi Kivity
2011-07-27T09:15:36Z

On 07/26/2011 02:31 PM, Xiao Guangrong wrote:
> 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
>
> @@ -3597,6 +3597,14 @@ static bool detect_write_misaligned(struct kvm_mmu_page *sp, gpa_t gpa,
>
> offset = offset_in_page(gpa);
> pte_size = sp->role.cr4_pae ? 8 : 4;
> +
> + /*
> + * Sometimes, the OS only writes the last one bytes to update status
> + * bits, for example, in linux, andb instruction is used in clear_bit().
> + */
> + if (sp->role.level == 1&& !(offset& (pte_size - 1))&& bytes == 1)
> + return false;
> +

Could be true for level > 1, no?

--
error compiling committee.c: too many arguments to function