Received-SPF: pass (google.com: domain of linux-kernel+bounces-202329-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Precedence: bulk
MIME-Version: 1.0
References: <20240531044644.768-4-ravi.bangoria@amd.com> <20240605114810.1304-1-ravi.bangoria@amd.com>
In-Reply-To: <20240605114810.1304-1-ravi.bangoria@amd.com>
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Wed, 5 Jun 2024 13:50:11 +0200
Message-ID: <CABgObfbq2sZ9U=8650EJq4FqiO=Dz2_mivOj_GponeNn2KyAVQ@mail.gmail.com>
Subject: Re: [PATCH] KVM: SNP: Fix LBR Virtualization for SNP guest
To: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: seanjc@google.com, nikunj.dadhania@amd.com, sraithal@amd.com, 
	thomas.lendacky@amd.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, 
	dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, 
	michael.roth@amd.com, pankaj.gupta@amd.com, kvm@vger.kernel.org, 
	linux-kernel@vger.kernel.org, santosh.shukla@amd.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Wed, Jun 5, 2024 at 1:49=E2=80=AFPM Ravi Bangoria <ravi.bangoria@amd.com=
> wrote:
>
> SEV-ES and thus SNP guest mandates LBR Virtualization to be _always_ ON.
> Although commit b7e4be0a224f ("KVM: SEV-ES: Delegate LBR virtualization
> to the processor") did the correct change for SEV-ES guests, it missed
> the SNP. Fix it.
>
> Reported-by: Srikanth Aithal <sraithal@amd.com>
> Fixes: b7e4be0a224f ("KVM: SEV-ES: Delegate LBR virtualization to the pro=
cessor")
> Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
> ---
> - SNP support was not present while I prepared the original patches and
>   that lead to this confusion. Sorry about that.

No problem, this is a semantic conflict and your original patches will
go in 6.10. Applied to kvm/next.

Paolo

>  arch/x86/kvm/svm/sev.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 7d401f8a3001..57291525e084 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2395,6 +2395,14 @@ static int snp_launch_update_vmsa(struct kvm *kvm,=
 struct kvm_sev_cmd *argp)
>                 }
>
>                 svm->vcpu.arch.guest_state_protected =3D true;
> +               /*
> +                * SEV-ES (and thus SNP) guest mandates LBR Virtualizatio=
n to
> +                * be _always_ ON. Enable it only after setting
> +                * guest_state_protected because KVM_SET_MSRS allows dyna=
mic
> +                * toggling of LBRV (for performance reason) on write acc=
ess to
> +                * MSR_IA32_DEBUGCTLMSR when guest_state_protected is not=
 set.
> +                */
> +               svm_enable_lbrv(vcpu);
>         }
>
>         return 0;
> --
> 2.45.1
>