linux-kernel - Re: [PATCH 3/3] kvm mmu: alloc shadow pages with __GFP

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Date:	Wed, 18 Feb 2009 14:03:34 +0000
From:	Avi Kivity <avi@...hat.com>
To:	Joerg Roedel <joerg.roedel@....com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] kvm mmu: alloc shadow pages with __GFP_ZERO

Joerg Roedel wrote:
> The assertion which the attached patch removes fails sometimes. Removing
> this assertion is the alternative solution to this problem ;-)
>
> From ca45f3a2e45cd7e76ca624bb1098329db8ff83ab Mon Sep 17 00:00:00 2001
> From: Joerg Roedel <joerg.roedel@....com>
> Date: Wed, 18 Feb 2009 14:51:13 +0100
> Subject: [PATCH] kvm mmu: remove assertion in kvm_mmu_alloc_page
>
> Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> ---
>  arch/x86/kvm/mmu.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index d93ecec..b226973 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -802,7 +802,6 @@ static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu,
>  	set_page_private(virt_to_page(sp->spt), (unsigned long)sp);
>  	list_add(&sp->link, &vcpu->kvm->arch.active_mmu_pages);
>  	INIT_LIST_HEAD(&sp->oos_link);
> -	ASSERT(is_empty_shadow_page(sp->spt));
>  	bitmap_zero(sp->slot_bitmap, KVM_MEMORY_SLOTS + KVM_PRIVATE_MEM_SLOTS);
>  	sp->multimapped = 0;
>  	sp->parent_pte = parent_pte;
>   

sp->spt is allocated using mmu_memory_cache_alloc(), which zeros the 
page.  How can the assertion fail?


-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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