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

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Message-ID: <20130128105903.GA22871@redhat.com>
Date:	Mon, 28 Jan 2013 12:59:03 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>,
	Alex Williamson <alex.williamson@...hat.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] kvm: IOMMU read-only mapping support

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@...hat.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.
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