From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Hou Wenlong <houwenlong93@linux.alibaba.com>
Subject: Re: [PATCH] KVM: x86: Inject #UD on "unsupported" hypercall if patching fails
Date: Mon, 13 Dec 2021 17:53:04 +0100 [thread overview]
Message-ID: <87wnk8v43z.fsf@redhat.com> (raw)
In-Reply-To: <20211210222903.3417968-1-seanjc@google.com>
Sean Christopherson <seanjc@google.com> writes:
> Ideally, KVM wouldn't patch at all; it's the guest's responsibility to
> identify and use the correct hypercall instruction (VMCALL vs. VMMCALL).
> Sadly, older Linux kernels prior to commit c1118b3602c2 ("x86: kvm: use
> alternatives for VMCALL vs. VMMCALL if kernel text is read-only") do the
> wrong thing and blindly use VMCALL, i.e. removing the patching would
> break running VMs with older kernels.
>
FWIW, we also use hypercall patching for Hyper-V emulation (when
HV_X64_MSR_HYPERCALL is written) and this complies with TLFS, we can't
get rid of this. It's a different 'patching' though...
--
Vitaly
prev parent reply other threads:[~2021-12-13 16:53 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-10 22:29 [PATCH] KVM: x86: Inject #UD on "unsupported" hypercall if patching fails Sean Christopherson
2021-12-10 22:41 ` Paolo Bonzini
2021-12-13 16:53 ` Vitaly Kuznetsov [this message]
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