linux-kernel - [PATCH v3 1/3] Correct asm VMXOFF side effects

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Date:   Sat,  4 Jul 2020 16:38:07 -0400
From:   "David P. Reed" <dpreed@...pplum.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     "David P. Reed" <dpreed@...pplum.com>,
        Andy Lutomirski <luto@...capital.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Allison Randal <allison@...utok.net>,
        Enrico Weigelt <info@...ux.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Martin Molnar <martin.molnar.programming@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Jann Horn <jannh@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v3 1/3] Correct asm VMXOFF side effects

Tell gcc that VMXOFF instruction clobbers condition codes
and memory when executed.
Also, correct original comments to remove kernel-doc syntax
per Randy Dunlap's request.

Suggested-by: Randy Dunlap <rdunlap@...radead.org>
Signed-off-by: David P. Reed <dpreed@...pplum.com>
---
 arch/x86/include/asm/virtext.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/virtext.h b/arch/x86/include/asm/virtext.h
index 9aad0e0876fb..0ede8d04535a 100644
--- a/arch/x86/include/asm/virtext.h
+++ b/arch/x86/include/asm/virtext.h
@@ -30,7 +30,7 @@ static inline int cpu_has_vmx(void)
 }
 
 
-/** Disable VMX on the current CPU
+/* Disable VMX on the current CPU
  *
  * vmxoff causes a undefined-opcode exception if vmxon was not run
  * on the CPU previously. Only call this function if you know VMX
@@ -38,7 +38,7 @@ static inline int cpu_has_vmx(void)
  */
 static inline void cpu_vmxoff(void)
 {
-	asm volatile ("vmxoff");
+	asm volatile ("vmxoff" ::: "cc", "memory");
 	cr4_clear_bits(X86_CR4_VMXE);
 }
 
@@ -47,7 +47,7 @@ static inline int cpu_vmx_enabled(void)
 	return __read_cr4() & X86_CR4_VMXE;
 }
 
-/** Disable VMX if it is enabled on the current CPU
+/* Disable VMX if it is enabled on the current CPU
  *
  * You shouldn't call this if cpu_has_vmx() returns 0.
  */
@@ -57,7 +57,7 @@ static inline void __cpu_emergency_vmxoff(void)
 		cpu_vmxoff();
 }
 
-/** Disable VMX if it is supported and enabled on the current CPU
+/* Disable VMX if it is supported and enabled on the current CPU
  */
 static inline void cpu_emergency_vmxoff(void)
 {
-- 
2.26.2