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AFNElJ9scDFq1TZoPz5X4TGrtPH3LvfCUVnBQabvOkuJTDXcjzHlLPF74zCBIiCYxtBQ+vxw+dXzpbSiQDQZ@lists.linux.dev X-Gm-Message-State: AOJu0YzlatH0PiB5xvzM/YD7zoKnmMTGqLMsFbDuYFwBzJEV1ArJzHqL AYpZafE9Xf4JX4U44yBQ6XM3GV8ESfQTNpOMiXcXApAQ+S8b07t1q6J78eCk/m+HzpSEhLGdwGI 54gzBOw== X-Received: from pfde26.prod.google.com ([2002:aa7:8c5a:0:b0:82f:dd9:c650]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:2449:b0:82c:21af:a7bf with SMTP id d2e1a72fcca58-83f33c25127mr4255212b3a.13.1778849724212; Fri, 15 May 2026 05:55:24 -0700 (PDT) Date: Fri, 15 May 2026 05:55:11 -0700 In-Reply-To: <27ba35fd-5563-4bbd-8f95-2285b50efa7a@linux.intel.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260514215355.1648463-1-seanjc@google.com> <20260514215355.1648463-4-seanjc@google.com> <27ba35fd-5563-4bbd-8f95-2285b50efa7a@linux.intel.com> Message-ID: Subject: Re: [PATCH v2 03/15] KVM: x86/xen: Don't truncate RAX when handling hypercall from protected guest From: Sean Christopherson To: Binbin Wu Cc: Paolo Bonzini , Vitaly Kuznetsov , Kiryl Shutsemau , David Woodhouse , Paul Durrant , Dave Hansen , Rick Edgecombe , kvm@vger.kernel.org, x86@kernel.org, linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, Yosry Ahmed , Kai Huang Content-Type: text/plain; charset="us-ascii" On Fri, May 15, 2026, Binbin Wu wrote: > > > On 5/15/2026 5:53 AM, Sean Christopherson wrote: > > Don't truncate RAX when handling a Xen hypercall for a guest with protected > > state, as KVM's ABI is to assume the guest is in 64-bit for such cases > > (the guest leaving garbage in 63:32 after a transition to 32-bit mode is > > far less likely than 63:32 being necessary to complete the hypercall). > > > > Fixes: b5aead0064f3 ("KVM: x86: Assume a 64-bit hypercall for guests with protected state") > > Signed-off-by: Sean Christopherson > > The patch looks good to me, but one question below. > > > --- > > arch/x86/kvm/xen.c | 6 +++--- > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c > > index 6d9be74bb673..895095dc684e 100644 > > --- a/arch/x86/kvm/xen.c > > +++ b/arch/x86/kvm/xen.c > > @@ -1678,15 +1678,14 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu) > > bool handled = false; > > u8 cpl; > > > > - input = (u64)kvm_register_read(vcpu, VCPU_REGS_RAX); > > - > > /* Hyper-V hypercalls get bit 31 set in EAX */ > > - if ((input & 0x80000000) && > > + if ((kvm_rax_read(vcpu) & 0x80000000) && > > kvm_hv_hypercall_enabled(vcpu)) > > return kvm_hv_hypercall(vcpu); > > > > longmode = is_64_bit_hypercall(vcpu); > > Is the variable name misleading? It most definitely is. However, @longmode is passed around quite a few locations in xen.c, and so I don't want to opportunistically fix this one variable. Though I'm definitely not opposed to a separate patch to rename them all to is_64bit or something. > If the vcpu is in compatible mode (when guest state is not protected), > it's in long mode, but the code goes to !longmode path. > > > if (!longmode) { > > + input = (u32)kvm_rax_read(vcpu); > > params[0] = (u32)kvm_rbx_read(vcpu); > > params[1] = (u32)kvm_rcx_read(vcpu); > > params[2] = (u32)kvm_rdx_read(vcpu); > > @@ -1696,6 +1695,7 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu) > > } > > else { > > #ifdef CONFIG_X86_64 > > + input = (u64)kvm_rax_read(vcpu); > > params[0] = (u64)kvm_rdi_read(vcpu); > > params[1] = (u64)kvm_rsi_read(vcpu); > > params[2] = (u64)kvm_rdx_read(vcpu); >