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x86/vmx: Remove .fixup usage

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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@infradead.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20211110101325.781308550@infradead.org
This commit is contained in:
Peter Zijlstra 2021-11-10 11:01:17 +01:00
parent c9a34c3f4e
commit 3e8ea7803a
1 changed files with 7 additions and 9 deletions
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16
arch/x86/kvm/vmx/vmx_ops.h
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@ -80,9 +80,11 @@ static __always_inline unsigned long __vmcs_readl(unsigned long field)
* @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 __vmcs_readl(unsigned long field)
"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;
}