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

Gleb Natapov
2013-01-28T10:59:03Z

On Fri, Jan 25, 2013 at 11:28:40AM +0800, Xiao Guangrong wrote:
> 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.
Why not just disallow changing memory region KVM_MEM_READONLY flag
without deleting the region?

--
Gleb.