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Re: [Xen-devel] [PATCH] x86/amd: fix crash as Xen Dom0 on AMD Trinity systems

On 05/31/2012 12:33 AM, Konrad Rzeszutek Wilk wrote:
Now, someone probably needs to paravirt the *safe_regs variants in case
something else decides to use them. I don't know what to do here, do I
want more paravirt code in there? No. I guess if this is done carefully
and cleanly, then it should be ok but it can't be done like that - it
needs to adhere to the current pv_cpu_ops thing which is already there.

Using the native variant seems the right thing to do.

I thought I was being told that Xen would trap and emulate the
rdmsr/wrmsr instructions.  I guess they don't want to do that for the

It does.
handful of performance-sensitive MSRs there are, but those don't use the
*_regs variants.

The underlaying issue (as I understand) was that .rdmsr_regs
(and the corresponding write) was NULL and that caused the crash.
This tiny patch should do it:

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 75f33b2..e74df95 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1116,7 +1116,10 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst = 
        .wbinvd = native_wbinvd,

        .read_msr = native_read_msr_safe,
+       .rdmsr_regs = native_rdmsr_safe_regs,
        .write_msr = xen_write_msr_safe,
+       .wrmsr_regs = native_wrmsr_safe_regs,
        .read_tsc = native_read_tsc,
        .read_pmc = native_read_pmc,

Acked-by: Andre Przywara <andre.przywara@xxxxxxx>

This works on the test machine.

Though I'd still like to have my original patch applied, because it makes the thing a bit cleaner.

And I made a patch to remove the {rd,wr}msr_regs hooks from paravirt_ops completely. Shall I send it out or do you want to make this part of larger patch series to clean up pvops?


Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany

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