From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
thomas.lendacky@amd.com, jmattson@google.com,
stable@vger.kernel.org
Subject: Re: [PATCH 10/11] KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to assembly
Date: Wed, 9 Nov 2022 16:04:04 +0000 [thread overview]
Message-ID: <Y2vPdDLAtZYMRoef@google.com> (raw)
In-Reply-To: <20221109145156.84714-11-pbonzini@redhat.com>
On Wed, Nov 09, 2022, Paolo Bonzini wrote:
> Restoration of the host IA32_SPEC_CTRL value is probably too late
> with respect to the return thunk training sequence.
>
> With respect to the user/kernel boundary, AMD says, "If software chooses
> to toggle STIBP (e.g., set STIBP on kernel entry, and clear it on kernel
> exit), software should set STIBP to 1 before executing the return thunk
> training sequence." I assume the same requirements apply to the guest/host
> boundary. The return thunk training sequence is in vmenter.S, quite close
> to the VM-exit. On hosts without V_SPEC_CTRL, however, the host's
> IA32_SPEC_CTRL value is not restored until much later.
>
> To avoid this, move the restoration of host SPEC_CTRL to assembly and,
> for consistency, move the restoration of the guest SPEC_CTRL as well.
> This is not particularly difficult, apart from some care to cover both
> 32- and 64-bit, and to share code between SEV-ES and normal vmentry.
>
> Cc: stable@vger.kernel.org
> Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
> Suggested-by: Jim Mattson <jmattson@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
Reviewed-by: Sean Christopherson <seanjc@google.com>
> +.ifnc _ASM_ARG1, _ASM_DI
> + /*
> + * Stash @svm in RDI early. On 32-bit, arguments are in RAX, RCX
> + * and RDX which are clobbered by RESTORE_GUEST_SPEC_CTRL.
> + */
> + mov %_ASM_ARG1, %_ASM_DI
> +.endif
Not technically needed since SEV-ES is 64-bit only, but that's a pre-exisiting
mess. I'll send a follow-up patch to #ifdef out the entire function and drop all
of this internal ifdeffery, and provide a stub in C code stub in C code so that
32-bit can link (and kill the VM if if the stub is reached).
next prev parent reply other threads:[~2022-11-09 16:04 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-09 14:51 [PATCH v3 00/11] KVM: SVM: fixes for vmentry code Paolo Bonzini
2022-11-09 14:51 ` [PATCH 01/11] KVM: x86: use a separate asm-offsets.c file Paolo Bonzini
2022-11-09 15:06 ` Sean Christopherson
2022-11-09 14:51 ` [PATCH 02/11] KVM: SVM: replace regs argument of __svm_vcpu_run with vcpu_svm Paolo Bonzini
2022-11-09 15:14 ` Sean Christopherson
2022-11-09 14:51 ` [PATCH 03/11] KVM: SVM: adjust register allocation for __svm_vcpu_run Paolo Bonzini
2022-11-09 15:20 ` Sean Christopherson
2022-11-09 16:04 ` Paolo Bonzini
2022-11-09 14:51 ` [PATCH 04/11] KVM: SVM: retrieve VMCB from assembly Paolo Bonzini
2022-11-09 15:25 ` Sean Christopherson
2022-11-09 14:51 ` [PATCH 05/11] KVM: SVM: remove unused field from struct vcpu_svm Paolo Bonzini
2022-11-09 15:25 ` Sean Christopherson
2022-11-09 14:51 ` [PATCH 06/11] KVM: SVM: remove dead field from struct svm_cpu_data Paolo Bonzini
2022-11-09 15:26 ` Sean Christopherson
2022-11-09 14:51 ` [PATCH 07/11] KVM: SVM: do not allocate struct svm_cpu_data dynamically Paolo Bonzini
2022-11-09 15:58 ` Sean Christopherson
2022-11-09 16:00 ` Paolo Bonzini
2022-11-09 14:51 ` [PATCH 08/11] KVM: SVM: move guest vmsave/vmload back to assembly Paolo Bonzini
2022-11-09 15:29 ` Sean Christopherson
2022-11-09 14:51 ` [PATCH 09/11] KVM: SVM: restore host save area from assembly Paolo Bonzini
2022-11-09 15:54 ` Sean Christopherson
2022-11-09 14:51 ` [PATCH 10/11] KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to assembly Paolo Bonzini
2022-11-09 16:04 ` Sean Christopherson [this message]
2022-11-09 14:51 ` [PATCH 11/11] x86, KVM: remove unnecessary argument to x86_virt_spec_ctrl and callers Paolo Bonzini
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