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

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Date:	Fri, 25 Jan 2013 13:28:16 +0900
From:	Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
To:	Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
Cc:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	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 Fri, 25 Jan 2013 12:59:12 +0900
Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp> wrote:

> > 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. ]
> 
> I'll look at the commit later, after the lunch break.

I've done!

So we need to do:

	if (npages && (GET_DIRTY || RDONLY))
		write protect

About sync_page, I'm not sure what is the best fix.

	Takuya

> 
> > 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.
> 
> So the change needed will be in arch/x86.
> 	in arch_commit_* one.
> 
> Right?
> 
> Note: I'm not touching arch_* memory slot APIs now because ARM KVM
> is coming now.  So no problem, the flags will be passed as before.
> 
> 	Takuya


-- 
Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
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