On Wed, May 20, 2020 at 11:17:25PM +0100, Andrew Cooper wrote: > 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 <jbeul...@suse.com> > > Reviewed-by: Roger Pau Monné <roger....@citrix.com> > > Acked-by: Andrew Cooper <andrew.coop...@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.
Hm, that's an interesting idea. There's also the _S3D device method that could give a false positive? (ie: a device having a _S3D method even when the DSDT doesn't have the _S3 method) Roger.
