[PATCH 14/22] x86,vmx: Remove .fixup usage

Peter Zijlstra
2021-11-05T17:20:09Z

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@infradead.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/include/asm/extable_fixup_types.h | 1 +
arch/x86/kvm/vmx/vmx_ops.h | 14 ++++++--------
2 files changed, 7 insertions(+), 8 deletions(-)

--- a/arch/x86/include/asm/extable_fixup_types.h
+++ b/arch/x86/include/asm/extable_fixup_types.h
@@ -42,5 +42,6 @@
#define EX_TYPE_EFAULT_REG (EX_TYPE_IMM_REG | EX_DATA_IMM(-EFAULT))
#define EX_TYPE_NEG_REG (EX_TYPE_IMM_REG | EX_DATA_IMM(-1))
#define EX_TYPE_ZERO_REG (EX_TYPE_IMM_REG | EX_DATA_IMM(0))
+#define EX_TYPE_ONE_REG (EX_TYPE_IMM_REG | EX_DATA_IMM(1))

#endif
--- 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;
}