linux-kernel - Re: [PATCH RFC v8 53/56] KVM: SVM: Make VMSAVE target area memory allocation SNP safe

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Date:   Wed, 1 Mar 2023 23:23:06 +0200
From:   Zhi Wang <zhi.wang.linux@...il.com>
To:     Michael Roth <michael.roth@....com>
Cc:     <kvm@...r.kernel.org>, <linux-coco@...ts.linux.dev>,
        <linux-mm@...ck.org>, <linux-crypto@...r.kernel.org>,
        <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <jroedel@...e.de>,
        <thomas.lendacky@....com>, <hpa@...or.com>, <ardb@...nel.org>,
        <pbonzini@...hat.com>, <seanjc@...gle.com>, <vkuznets@...hat.com>,
        <jmattson@...gle.com>, <luto@...nel.org>,
        <dave.hansen@...ux.intel.com>, <slp@...hat.com>,
        <pgonda@...gle.com>, <peterz@...radead.org>,
        <srinivas.pandruvada@...ux.intel.com>, <rientjes@...gle.com>,
        <dovmurik@...ux.ibm.com>, <tobin@....com>, <bp@...en8.de>,
        <vbabka@...e.cz>, <kirill@...temov.name>, <ak@...ux.intel.com>,
        <tony.luck@...el.com>, <marcorr@...gle.com>,
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        <alpergun@...gle.com>, <dgilbert@...hat.com>, <jarkko@...nel.org>,
        <ashish.kalra@....com>, <nikunj.dadhania@....com>
Subject: Re: [PATCH RFC v8 53/56] KVM: SVM: Make VMSAVE target area memory
 allocation SNP safe

On Mon, 20 Feb 2023 12:38:44 -0600
Michael Roth <michael.roth@....com> wrote:

> From: Ashish Kalra <ashish.kalra@....com>
> 
> Implement a workaround for an SNP erratum where the CPU will incorrectly
> signal an RMP violation #PF if a hugepage (2mb or 1gb) collides with the
> RMP entry of the VMSAVE target page.
> 
> When SEV-SNP is globally enabled, the CPU marks the VMSAVE target page
> as "InUse" while the VMSAVE instruction is executing. If another
> CPU writes to a different page in the same 2MB region while the VMSAVE
> is executing, the CPU will throw an RMP violation #PF.
> 
> Use the snp safe generic allocator for allocating the VMSA target
> page which will ensure that the page returned is not a hugepage, as it
> is already being used for the allocating the VMCB, VMSA and AVIC backing
> page.
> 

This should be merged with patch where implements the snp_safe_alloc_page().

> Co-developed-by: Marc Orr <marcorr@...gle.com>
> Signed-off-by: Marc Orr <marcorr@...gle.com>
> Reported-by: Alper Gun <alpergun@...gle.com>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> Signed-off-by: Michael Roth <michael.roth@....com>
> ---
>  arch/x86/kvm/svm/svm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 3fe5f13b5f3a..8bda31a61757 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -665,7 +665,7 @@ static int svm_cpu_init(int cpu)
>  	int ret = -ENOMEM;
>  
>  	memset(sd, 0, sizeof(struct svm_cpu_data));
> -	sd->save_area = alloc_page(GFP_KERNEL | __GFP_ZERO);
> +	sd->save_area = snp_safe_alloc_page(NULL);
>  	if (!sd->save_area)
>  		return ret;
>