linux-kernel - [PATCH v2 15/23] x86,vmx: Remove .fixup usage

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Message-ID: <20211110101325.781308550@infradead.org>
Date:   Wed, 10 Nov 2021 11:01:17 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        jpoimboe@...hat.com, mark.rutland@....com, dvyukov@...gle.com,
        seanjc@...gle.com, pbonzini@...hat.com, mbenes@...e.cz
Subject: [PATCH v2 15/23] x86,vmx: Remove .fixup usage

In the vmread exceptin path, use the, thus far, unused output register
to push the @fault argument onto the stack. This, in turn, enables the
exception handler to not do pushes and only modify that register when
an exception does occur.

As noted by Sean the input constraint needs to be changed to "=&r" to
avoid the value and field occupying the same register.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/vmx/vmx_ops.h |   16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

--- a/arch/x86/kvm/vmx/vmx_ops.h
+++ b/arch/x86/kvm/vmx/vmx_ops.h
@@ -80,9 +80,11 @@ static __always_inline unsigned long __v
 		      * @field, and bounce through the trampoline to preserve
 		      * volatile registers.
 		      */
-		     "push $0\n\t"
+		     "xorl %k1, %k1\n\t"
+		     "2:\n\t"
+		     "push %1\n\t"
 		     "push %2\n\t"
-		     "2:call vmread_error_trampoline\n\t"
+		     "call vmread_error_trampoline\n\t"
 
 		     /*
 		      * Unwind the stack.  Note, the trampoline zeros out the
@@ -93,13 +95,9 @@ static __always_inline unsigned long __v
 		     "3:\n\t"
 
 		     /* VMREAD faulted.  As above, except push '1' for @fault. */
-		     ".pushsection .fixup, \"ax\"\n\t"
-		     "4: push $1\n\t"
-		     "push %2\n\t"
-		     "jmp 2b\n\t"
-		     ".popsection\n\t"
-		     _ASM_EXTABLE(1b, 4b)
-		     : ASM_CALL_CONSTRAINT, "=r"(value) : "r"(field) : "cc");
+		     _ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_ONE_REG, %1)
+
+		     : ASM_CALL_CONSTRAINT, "=&r"(value) : "r"(field) : "cc");
 	return value;
 }