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Re: [PATCH] xen/acpi-processor: fix _CST detection using undersized evaluation buffer
- To: "David Thomson (dt@xxxxxxxxx)" <dt@xxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 24 Feb 2026 10:21:24 +0100
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- Cc: boris.ostrovsky@xxxxxxxxxx, sstabellini@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, jgross@xxxxxxxx
- Delivery-date: Tue, 24 Feb 2026 09:21:29 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 24.02.2026 10:10, David Thomson (dt@xxxxxxxxx) wrote:
>> I understand you reflect original behavior in this regard, but why involve
>> any
>> ACPI function here at all when pblk is non-zero? I.e. why not swap the
>> operands
>> of && ? Object evaluation could have wanted side effects (in which case,
>> however, some different change would be needed here), but checking for method
>> presence surely hasn't.
>>
> You're right on both counts. The original evaluate_object() call at least had
> the appearance of wanting the result (even though buf was undersized and the
> result was never used). A pure presence check has no such pretense. Swapping
> the operands is the obvious improvement. I think dropping the _CST check
> entirely is also defensible since C-state support is confirmed when pblk is
> set. But I'm not certain there's no edge case where pblk is non-zero and _CST
> is also not present, so I'd defer to your judgement.
>
> Would you prefer:
> a) if (pblk && acpi_has_method(handle, "_CST"))
> b) just if (pblk)
I don't think b) is correct, so a) please (albeit suitably adjusted to really
only
flip the operands from what your original patch had).
Jan
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