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Re: [PATCH] x86/amd: Convert wrmsr_amd_safe() to use asm goto()
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 4 Apr 2025 09:48:46 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 04 Apr 2025 07:48:57 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 03.04.2025 19:57, Andrew Cooper wrote:
> Bloat-o-meter reports:
>
> add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-29 (-29)
> Function old new delta
> _probe_mask_msr 99 94 -5
> init_amd 2418 2394 -24
>
> but that's because .fixup doesn't contain sized/typed symbols. This also
> drops two "mov -EFAULT, %reg; jmp ...;" sequences too. The net saving is -50.
>
> wrmsr_amd_safe()'s return value is only checked against 0 (if at all), and
> because of this, the compiler can now avoid manifesting 0/-EFAULT entirely,
> and the %[fault] label simply lands on the right basic block.
>
> Convert to Xen style while rewriting.
>
> No functional change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>
> Slightly RFC. We use -EIO elsewhere for this purpose, and nothing in this
> logic cares.
{rd,wr}msr_safe() both use -EFAULT. What's "elsewhere" here?
> I was pleasently surprised by the manifestation of -EFAULT going away
> entirely.
I fear I don't understand this, given the -EFAULT is still there in the
new code.
Irrespective of these remarks:
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Jan
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