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Re: [XEN PATCH v1] x86/APIC: Read Error Status Register correctly


  • To: Javi Merino <javi.merino@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Tue, 26 Nov 2024 20:07:52 +0000
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  • Cc: Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Tue, 26 Nov 2024 20:08:07 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 26/11/2024 5:06 pm, Javi Merino wrote:
> The logic to read the APIC_ESR was copied from linux in a commit from
> 2002: 4676bbf96dc8 (bitkeeper revision
> 1.2 (3ddb79c9KusG02eh7i-uXkgY0IksKA), 2002-11-20).  In linux 3.14,
> this logic was fixed to follow the Intel SDM (see commit
> 60283df7ac26 (x86/apic: Read Error Status Register correctly,
> 2014-01-14) in the linux kernel).  The Intel(r) 64 and IA-32
> Architectures Software Develover's Manual currently says
> in Volume 3, Section 12.5.3:
>
>   Before attempt to read from the ESR, software should first write to
>   it. (The value written does not affect the values read subsequently;
>   only zero may be written in x2APIC mode.) This write clears any
>   previously logged errors and updates the ESR with any errors
>   detected since the last write to the ESR. This write also rearms the
>   APIC error interrupt triggering mechanism.
>
> Update error_interrupt() to remove the first read and follow the Intel
> manual.
>
> Signed-off-by: Javi Merino <javi.merino@xxxxxxxxx>

In Linux, this bugfix was further corrected with
https://lore.kernel.org/lkml/alpine.LFD.2.11.1404011300010.27402@xxxxxxxxxxxxxxxxxxxx/

However, Xen being 64-bit only doesn't care about the Pentium 3AP errata
with writing to ESR.

I'm tempted to take this patch as-is, then do a followup on top to
remove the remnants of the Pentium errata from Xen.  I don't think it's
interesting to take bugfixes to bugfixes simply to delete them right after.

Thoughts?

~Andrew



 


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