linux-kernel - Re: [PATCH 10/11] KVM: MMU: fix detecting misaligned accessed

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Date:	Wed, 27 Jul 2011 12:15:29 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 10/11] KVM: MMU: fix detecting misaligned accessed

On 07/26/2011 02:31 PM, Xiao Guangrong wrote:
> Sometimes, we only modify the last one byte of a pte to update status bit,
> for example, clear_bit is used to clear r/w bit in linux kernel and 'andb'
> instruction is used in this function, in this case, kvm_mmu_pte_write will
> treat it as misaligned access, and the shadow page table is zapped
>
> @@ -3597,6 +3597,14 @@ static bool detect_write_misaligned(struct kvm_mmu_page *sp, gpa_t gpa,
>
>   	offset = offset_in_page(gpa);
>   	pte_size = sp->role.cr4_pae ? 8 : 4;
> +
> +	/*
> +	 * Sometimes, the OS only writes the last one bytes to update status
> +	 * bits, for example, in linux, andb instruction is used in clear_bit().
> +	 */
> +	if (sp->role.level == 1&&  !(offset&  (pte_size - 1))&&  bytes == 1)
> +		return false;
> +

Could be true for level > 1, no?

-- 
error compiling committee.c: too many arguments to function

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