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Re: [Xen-devel] [PATCH] x86: clear RDRAND CPUID bit on AMD family 15h/16h
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 29 Aug 2019 12:42:47 +0100
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- Cc: Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 29 Aug 2019 11:43:00 +0000
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On 29/08/2019 10:28, Jan Beulich wrote:
> Inspired by Linux commit c49a0a80137c7ca7d6ced4c812c9e07a949f6f24:
>
> There have been reports of RDRAND issues after resuming from suspend on
> some AMD family 15h and family 16h systems. This issue stems from a BIOS
> not performing the proper steps during resume to ensure RDRAND continues
> to function properly.
>
> Update the CPU initialization to clear the RDRAND CPUID bit for any family
> 15h and 16h processor that supports RDRAND. If it is known that the family
> 15h or family 16h system does not have an RDRAND resume issue or that the
> system will not be placed in suspend, the "cpuid=rdrand" kernel parameter
> can be used to stop the clearing of the RDRAND CPUID bit.
>
> Note, that clearing the RDRAND CPUID bit does not prevent a processor
> that normally supports the RDRAND instruction from executing it. So any
> code that determined the support based on family and model won't #UD.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Slightly RFC, in particular because of the change to parse_xen_cpuid():
> Alternative approach suggestions are welcome.
This issue was on my radar, but I hadn't got around to starting a patch yet.
I was wondering if we could perhaps default it to whether S3 was
available, but looking at the code which prints "ACPI sleep modes: S3",
it doesn't appear to be related to any real ACPI information.
~Andrew
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