linux-kernel - Re: [PATCH v2 16/23] x86,vmx: Provide asm-goto-output vmread

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Message-ID: <YbcbbGW2GcMx6KpD@hirez.programming.kicks-ass.net>
Date:   Mon, 13 Dec 2021 11:07:40 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, jpoimboe@...hat.com,
        mark.rutland@....com, dvyukov@...gle.com, seanjc@...gle.com,
        pbonzini@...hat.com, mbenes@...e.cz
Subject: Re: [PATCH v2 16/23] x86,vmx: Provide asm-goto-output vmread


Here's a version that doesn't make clang ICE..

Paolo, since this doesn't really depend on the .fixup removal series,
feel free to collect it in the kvm tree or somesuch.

---
Subject: x86/vmx: Provide asm-goto-output vmread
From: Peter Zijlstra <peterz@...radead.org>
Date: Wed, 10 Nov 2021 11:01:18 +0100

Use asm-goto-output for smaller fast path code.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/kvm/vmx/vmx_ops.h |   27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

--- a/arch/x86/kvm/vmx/vmx_ops.h
+++ b/arch/x86/kvm/vmx/vmx_ops.h
@@ -71,6 +71,31 @@ static __always_inline unsigned long __v
 {
 	unsigned long value;
 
+#ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
+
+	asm_volatile_goto("1: vmread %[field], %[output]\n\t"
+			  "jna %l[do_fail]\n\t"
+
+			  _ASM_EXTABLE(1b, %l[do_exception])
+
+			  : [output] "=r" (value)
+			  : [field] "r" (field)
+			  : "cc"
+			  : do_fail, do_exception);
+
+	return value;
+
+do_fail:
+	WARN_ONCE(1, "kvm: vmread failed: field=%lx\n", field);
+	pr_warn_ratelimited("kvm: vmread failed: field=%lx\n", field);
+	return 0;
+
+do_exception:
+	kvm_spurious_fault();
+	return 0;
+
+#else /* !CONFIG_CC_HAS_ASM_GOTO_OUTPUT */
+
 	asm volatile("1: vmread %2, %1\n\t"
 		     ".byte 0x3e\n\t" /* branch taken hint */
 		     "ja 3f\n\t"
@@ -99,6 +124,8 @@ static __always_inline unsigned long __v
 
 		     : ASM_CALL_CONSTRAINT, "=&r"(value) : "r"(field) : "cc");
 	return value;
+
+#endif /* CONFIG_CC_HAS_ASM_GOTO_OUTPUT */
 }
 
 static __always_inline u16 vmcs_read16(unsigned long field)