Re: [RFC][PATCH 15/22] x86,vmx: Remove .fixup usage

Paolo Bonzini
2021-11-04T18:54:09Z

On 11/4/21 17:47, Peter Zijlstra wrote:
> 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>
> ---
> 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;
> }
>
>

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>