On Monday, December 30, 2019 at 1:44:13 PM UTC-5, qubes123 wrote:
>
> Answering to your earlier question, my CPU capability information bits
> change like this after suspend:
>
> (XEN) Entering ACPI S3 state.
> (XEN) AMD-Vi: Applying erratum 746 workaround for IOMMU at 0000:00:00.2
> (XEN) Finishing wakeup from ACPI S3 state.
> (XEN) CPU0: cap[ 1] is 3e98320b (expected b698320b)
> (XEN) Missing previously available feature(s).
> (XEN) Enabling non-boot CPUs ...
>
> Without the patch this result in xen panic.
>
> PS: my patch looks like this (it will show the CPUID capability bits
> changing in the hypervisor log)
>
> diff -ruN a/xen/arch/x86/acpi/power.c b/xen/arch/x86/acpi/power.c
> --- a/xen/arch/x86/acpi/power.c 2019-12-15 18:26:11.183000000 +0100
> +++ b/xen/arch/x86/acpi/power.c 2019-12-15 18:23:15.439000000 +0100
> @@ -257,7 +257,7 @@
> microcode_resume_cpu(0);
>
> if ( !recheck_cpu_features(0) )
> - panic("Missing previously available feature(s).");
> + printk(XENLOG_ERR "Missing previously available
> feature(s).\n");
>
> /* Re-enabled default NMI/#MC use of MSR_SPEC_CTRL. */
> ci->spec_ctrl_flags |= (default_spec_ctrl_flags & SCF_ist_wrmsr);
>
Interesting. This call to recheck_cpu_features appears to be a check/panic
that is also in Qubes R4.0, and was backported to Xen 4.8.3 last year:
https://github.com/QubesOS/qubes-vmm-xen/commit/c921e46e9e18cd1cfa1347289db4c2f61b8f686a#diff-9ff8c82836adac8412cd8ac4afdf8cae
q123 - do you happen to know what the exact two flag bits that changed
represent in the cpu features? I wonder if the true issue is something not
being properly preserved during the suspend, or properly re-initialized
during the resume.
Brendan
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