Re: [PATCH 0/2] kvm: IOMMU read-only mapping support

Xiao Guangrong
2013-01-25T03:28:48Z

On 01/25/2013 09:17 AM, Takuya Yoshikawa wrote:
> On Thu, 24 Jan 2013 15:03:57 -0700
> Alex Williamson <alex.williamson@redhat.com> wrote:
>
>> A couple patches to make KVM IOMMU support honor read-only mappings.
>> This causes an un-map, re-map when the read-only flag changes and
>> makes use of it when setting IOMMU attributes. Thanks,
>
> Looks good to me.
>
> I think I can naturally update my patch after this gets merged.
>

Please wait.

The commit c972f3b1 changed the write-protect behaviour - it does
wirte-protection only when dirty flag is set.
[ I did not see this commit when we discussed the problem before. ]

Further more, i notice that write-protect is not enough, when do sync
shadow page:

FNAME(sync_page):

host_writable = sp->spt[i] & SPTE_HOST_WRITEABLE;

set_spte(vcpu, &sp->spt[i], pte_access,
PT_PAGE_TABLE_LEVEL, gfn,
spte_to_pfn(sp->spt[i]), true, false,
host_writable);

It sets spte based on the old value that means the readonly flag check
is missed. We need to call kvm_arch_flush_shadow_all under this case.