From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <jbeulich@suse.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH v5] x86: clear RDRAND CPUID bit on AMD family 15h/16h
Date: Wed, 20 May 2020 23:17:25 +0100 [thread overview]
Message-ID: <e2cf9d9e-492d-fa24-0e9c-bf62b6704b34@citrix.com> (raw)
In-Reply-To: <4f76749b-54bd-7c39-6c90-279ce25cb57c@suse.com>
On 18/05/2020 14:19, 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.
>
> Warn if no explicit choice was given on affected hardware.
>
> Check RDRAND functions at boot as well as after S3 resume (the retry
> limit chosen is entirely arbitrary).
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
> ---
> Still slightly RFC, and still in particular because of the change to
> parse_xen_cpuid(): Alternative approach suggestions are welcome. But now
> also because with many CPUs there may now be a lot of warnings in case
> of issues.
It would still be nice if we could find a better way of determining
whether S3 is supported on the platform, which would at least let us
sort server and client platforms.
A straight string search for _S3 in the DSDT does look to be effective,
on a sample of 5 boxes I've tried.
~Andrew
next prev parent reply other threads:[~2020-05-20 22:17 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-18 13:19 [PATCH v5] x86: clear RDRAND CPUID bit on AMD family 15h/16h Jan Beulich
2020-05-20 22:17 ` Andrew Cooper [this message]
2020-05-21 9:47 ` Roger Pau Monné
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