linux-kernel - Re: [PATCH RFC v9 04/51] KVM: x86: Determine shared/private faults using a configurable mask

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Date:   Tue, 20 Jun 2023 15:36:00 -0500
From:   Michael Roth <michael.roth@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <kvm@...r.kernel.org>, <linux-coco@...ts.linux.dev>,
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Subject: Re: [PATCH RFC v9 04/51] KVM: x86: Determine shared/private faults
 using a configurable mask

On Mon, Jun 19, 2023 at 06:27:03PM +0200, Borislav Petkov wrote:
> On Sun, Jun 11, 2023 at 11:25:12PM -0500, Michael Roth wrote:
> > This will be used to determine whether or not an #NPF should be serviced
> > using a normal page vs. a guarded/gmem one.
> > 
> > Signed-off-by: Michael Roth <michael.roth@....com>
> > ---
> >  arch/x86/include/asm/kvm_host.h |  7 +++++++
> >  arch/x86/kvm/mmu/mmu_internal.h | 35 ++++++++++++++++++++++++++++++++-
> >  2 files changed, 41 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index b3bd24f2a390..c26f76641121 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1445,6 +1445,13 @@ struct kvm_arch {
> >  	 */
> >  #define SPLIT_DESC_CACHE_MIN_NR_OBJECTS (SPTE_ENT_PER_PAGE + 1)
> >  	struct kvm_mmu_memory_cache split_desc_cache;
> > +
> > +	/*
> > +	 * When set, used to determine whether a fault should be treated as
> 	   ^^^^^^^^
> 
> And when not set? Invalid?
> 
> I guess so, judging by the code below.

Yes, or more specifically, "When not set, treat the value set by
userspace via KVM_SET_MEMORY_ATTRIBUTES as the authority on whether to
treat a fault as private or not. In this case, KVM_EXIT_MEMORY_FAULT
events won't be generated, so there will never be a mismatch between
what hardware indicates via page fault flags vs. what software has
assigned via KVM_SET_MEMORY_ATTRIBUTES".

-Mike

> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette