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From:   Peter Gonda <pgonda@google.com>
Date:   Tue, 14 Sep 2021 16:03:54 -0600
Message-ID: <CAMkAt6rnUUS9t1Z73dqZ0_3iUmyRxz5hJmZ+A3vQ34t3N=JAFQ@mail.gmail.com>
Subject: Re: [PATCH 1/2] KVM: SEV: Pin guest memory for write for RECEIVE_UPDATE_DATA
To:     Sean Christopherson <seanjc@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm list <kvm@vger.kernel.org>,
        linux-kernel@vger.kernel.org, Marc Orr <marcorr@google.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Brijesh Singh <brijesh.singh@amd.com>,
        Masahiro Kozuka <masa.koz@kozuka.jp>
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On Tue, Sep 14, 2021 at 3:09 PM Sean Christopherson <seanjc@google.com> wrote:
>
> Require the target guest page to be writable when pinning memory for
> RECEIVE_UPDATE_DATA.  Per the SEV API, the PSP writes to guest memory:
>
>   The result is then encrypted with GCTX.VEK and written to the memory
>   pointed to by GUEST_PADDR field.
>
> Fixes: 15fb7de1a7f5 ("KVM: SVM: Add KVM_SEV_RECEIVE_UPDATE_DATA command")
> Cc: stable@vger.kernel.org
> Cc: Peter Gonda <pgonda@google.com>
> Cc: Marc Orr <marcorr@google.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Peter Gonda <pgonda@google.com>

> ---
>  arch/x86/kvm/svm/sev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 75e0b21ad07c..95228ba3cd8f 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1464,7 +1464,7 @@ static int sev_receive_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp)
>
>         /* Pin guest memory */
>         guest_page = sev_pin_memory(kvm, params.guest_uaddr & PAGE_MASK,
> -                                   PAGE_SIZE, &n, 0);
> +                                   PAGE_SIZE, &n, 1);
>         if (IS_ERR(guest_page)) {
>                 ret = PTR_ERR(guest_page);
>                 goto e_free_trans;

Not sure how common this is but adding a comment like this could help
with readability:
+                                   PAGE_SIZE, &n, /* write= */ 1);


> --
> 2.33.0.309.g3052b89438-goog
>