linux-kernel - [PATCH v4 1/6] KVM: x86: Play nice with protected guests in complete_hypercall

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Message-ID: <20241128004344.4072099-2-seanjc@google.com>
Date: Wed, 27 Nov 2024 16:43:39 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Tom Lendacky <thomas.lendacky@....com>, Binbin Wu <binbin.wu@...ux.intel.com>, 
	Isaku Yamahata <isaku.yamahata@...el.com>, Kai Huang <kai.huang@...el.com>, 
	Xiaoyao Li <xiaoyao.li@...el.com>
Subject: [PATCH v4 1/6] KVM: x86: Play nice with protected guests in complete_hypercall_exit()

Use is_64_bit_hypercall() instead of is_64_bit_mode() to detect a 64-bit
hypercall when completing said hypercall.  For guests with protected state,
e.g. SEV-ES and SEV-SNP, KVM must assume the hypercall was made in 64-bit
mode as the vCPU state needed to detect 64-bit mode is unavailable.

Hacking the sev_smoke_test selftest to generate a KVM_HC_MAP_GPA_RANGE
hypercall via VMGEXIT trips the WARN:

  ------------[ cut here ]------------
  WARNING: CPU: 273 PID: 326626 at arch/x86/kvm/x86.h:180 complete_hypercall_exit+0x44/0xe0 [kvm]
  Modules linked in: kvm_amd kvm ... [last unloaded: kvm]
  CPU: 273 UID: 0 PID: 326626 Comm: sev_smoke_test Not tainted 6.12.0-smp--392e932fa0f3-feat #470
  Hardware name: Google Astoria/astoria, BIOS 0.20240617.0-0 06/17/2024
  RIP: 0010:complete_hypercall_exit+0x44/0xe0 [kvm]
  Call Trace:
   <TASK>
   kvm_arch_vcpu_ioctl_run+0x2400/0x2720 [kvm]
   kvm_vcpu_ioctl+0x54f/0x630 [kvm]
   __se_sys_ioctl+0x6b/0xc0
   do_syscall_64+0x83/0x160
   entry_SYSCALL_64_after_hwframe+0x76/0x7e
   </TASK>
  ---[ end trace 0000000000000000 ]---

Fixes: b5aead0064f3 ("KVM: x86: Assume a 64-bit hypercall for guests with protected state")
Cc: stable@...r.kernel.org
Cc: Tom Lendacky <thomas.lendacky@....com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2e713480933a..0b2fe4aa04a2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9976,7 +9976,7 @@ static int complete_hypercall_exit(struct kvm_vcpu *vcpu)
 {
 	u64 ret = vcpu->run->hypercall.ret;
 
-	if (!is_64_bit_mode(vcpu))
+	if (!is_64_bit_hypercall(vcpu))
 		ret = (u32)ret;
 	kvm_rax_write(vcpu, ret);
 	++vcpu->stat.hypercalls;
-- 
2.47.0.338.g60cca15819-goog