linux-kernel - [RFC][PATCH 15/22] x86,vmx: Remove .fixup usage

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Message-ID: <20211104165525.408049586@infradead.org>
Date:   Thu, 04 Nov 2021 17:47:44 +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: [RFC][PATCH 15/22] 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.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/kvm/vmx/vmx_ops.h |   14 ++++++--------
 1 file changed, 6 insertions(+), 8 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
@@ -93,12 +95,8 @@ 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_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_ONE_REG, %1)
+
 		     : ASM_CALL_CONSTRAINT, "=r"(value) : "r"(field) : "cc");
 	return value;
 }