Re: [PATCH v2 3/8] x86/hyperv: set MTRR state when running as SEV-SNP Hyper-V guest

[Juergen Gross <jgross@xxxxxxxx>]

On 13.02.23 02:07, Michael Kelley (LINUX) wrote:
> From: Juergen Gross <jgross@xxxxxxxx> Sent: Wednesday, February 8, 2023 11:22 PM
> > In order to avoid mappings using the UC- cache attribute, set the
> > MTRR state to use WB caching as the default.
> >
> > This is needed in order to cope with the fact that PAT is enabled,
> > while MTRRs are disabled by the hypervisor.
> >
> > Fixes: 90b926e68f50 ("x86/pat: Fix pat_x_mtrr_type() for MTRR disabled case")
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> > V2:
> > - new patch
> > ---
> >   arch/x86/kernel/cpu/mshyperv.c | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> >
> > diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> > index 46668e255421..51e47dc0e987 100644
> > --- a/arch/x86/kernel/cpu/mshyperv.c
> > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > @@ -34,6 +34,7 @@
> >   #include <clocksource/hyperv_timer.h>
> >   #include <asm/numa.h>
> >   #include <asm/coco.h>
> > +#include <asm/mtrr.h>
> >
> >   /* Is Linux running as the root partition? */
> >   bool hv_root_partition;
> > @@ -335,6 +336,13 @@ static void __init ms_hyperv_init_platform(void)
> >   			static_branch_enable(&isolation_type_snp);
> >   #ifdef CONFIG_SWIOTLB
> >   			swiotlb_unencrypted_base = ms_hyperv.shared_gpa_boundary;
> > +#endif
>
> Unfortunately, Hyper-V does not filter out the MTRR flag from the
> CPUID leaf, so this code also needs
>
> 			setup_clear_cpu_cap(X86_FEATURE_MTRR);
>
> before calling mtrr_overwrite_state().  I've got a bug filed for the
> Hyper-V team to fix the flag, but clearing the feature here solves the
> problem regardless.

Okay, will add it.

> > +#ifdef CONFIG_MTRR
>
> Hopefully this #ifdef can go away, per my comment in Patch 2 of
> the series.

As said already, fine with me.


Juergen

Attachment: OpenPGP_0xB0DE9DD628BF132F.asc
Description: OpenPGP public key

Attachment: OpenPGP_signature
Description: OpenPGP digital signature