linux-kernel - Re: [PATCH v2] KVM: mmu: allow page tables to be in read-only slots

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Date:	Mon, 09 Sep 2013 12:12:23 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kvm@...r.kernel.org,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2] KVM: mmu: allow page tables to be in read-only slots

Il 08/09/2013 11:04, Gleb Natapov ha scritto:
> On Thu, Sep 05, 2013 at 02:21:53PM +0200, Paolo Bonzini wrote:
>> Page tables in a read-only memory slot will currently cause a triple
>> fault when running with shadow paging, because the page walker uses
>> gfn_to_hva and it fails on such a slot.
>>
>> TianoCore uses such a page table.  The idea is that, on real hardware,
>> the firmware can already run in 64-bit flat mode when setting up the
>> memory controller.  Real hardware seems to be fine with that as long as
>> the accessed/dirty bits are set.  Thus, this patch saves whether the
>> slot is readonly, and later checks it when updating the accessed and
>> dirty bits.
>>
>> Note that this scenario is not supported by NPT at all, as explained by
>> comments in the code.
>>
>> Cc: stable@...r.kernel.org
>> Cc: kvm@...r.kernel.org
>> Cc: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
>> Cc: Gleb Natapov <gleb@...hat.com>
>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> I would prefer to change gfn_to_hva_read() to gfn_to_hva_prot() in this
> patch already, it will not make it any bigger

Sure.

Paolo

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