[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH] x86: clear RDRAND CPUID bit on AMD family 15h/16h



On 29.08.19 13:42, Andrew Cooper wrote:
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.

Yeah, but it will no longer see random numbers after resume.


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.

Wouldn't it make more sense to inhibit suspend/resume instead?

I'm quite sure a machine running Xen is very rarely put to S3.


Juergen

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel

 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.