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

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Message-ID: <5101FBE8.9000206@linux.vnet.ibm.com>
Date:	Fri, 25 Jan 2013 11:28:40 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
CC:	Alex Williamson <alex.williamson@...hat.com>, gleb@...hat.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] kvm: IOMMU read-only mapping support

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.

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