linux-kernel - Re: [RFC PATCH 05/16] KVM: arm64: Introduce "struct kvm_page

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Message-ID: <aK4DwtuQtzYvRei-@google.com>
Date: Tue, 26 Aug 2025 11:58:10 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Oliver Upton <oliver.upton@...ux.dev>
Cc: Marc Zyngier <maz@...nel.org>, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	James Houghton <jthoughton@...gle.com>
Subject: Re: [RFC PATCH 05/16] KVM: arm64: Introduce "struct kvm_page_fault"
 for tracking abort state

On Thu, Aug 21, 2025, Oliver Upton wrote:
> Hey Sean,
> 
> On Thu, Aug 21, 2025 at 02:00:31PM -0700, Sean Christopherson wrote:
> > Add and use a kvm_page_fault structure to track state when handling a
> > guest abort.  Collecting everything in a single structure will enable a
> > variety of cleanups (reduce the number of params passed to helpers), and
> > will pave the way toward using "struct kvm_page_fault" in arch-neutral KVM
> > code, e.g. to consolidate logic for KVM_EXIT_MEMORY_FAULT.
> > 
> > No functional change intended.
> > 
> > Cc: James Houghton <jthoughton@...gle.com>
> > Link: https://lore.kernel.org/all/20250618042424.330664-1-jthoughton@google.com
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> >  arch/arm64/include/asm/kvm_host.h |  18 ++++
> >  arch/arm64/kvm/mmu.c              | 143 ++++++++++++++----------------
> >  2 files changed, 87 insertions(+), 74 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 2f2394cce24e..4623cbc1edf4 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -413,6 +413,24 @@ struct kvm_vcpu_fault_info {
> >  	u64 disr_el1;		/* Deferred [SError] Status Register */
> >  };
> >  
> > +struct kvm_page_fault {
> > +	const u64 esr;
> > +	const bool exec;
> > +	const bool write;
> > +	const bool is_perm;
> 
> Hmm... these might be better represented as predicates that take a
> pointer to this struct and we just compute it based on ESR. That'd have
> the benefit in the arch-neutral code where 'struct kvm_page_fault' is an
> opaque type and we don't need to align field names/types.

We'd need to align function names/types though, so to some extent it's six of one,
half dozen of the other.  My slight preference would be to require kvm_page_fault
to have certain fields, but I'm ok with making kvm_page_fault opaque to generic
code and instead adding arch APIs.  Having a handful of wrappers in x86 isn't the
end of the world, and it would be more familiar for pretty much everyone.

> > +	phys_addr_t fault_ipa; /* The address we faulted on */
> > +	phys_addr_t ipa; /* Always the IPA in the L1 guest phys space */
> 
> NYC, but this also seems like a good opportunity to rename + retype
> these guys. Specifically:
> 
> 	fault_ipa => ipa
> 	ipa => canonical_ipa
> 
> would clarify these and align with the verbiage we currently use to talk
> about nested.

Heh, I'm so screwed.  x86's use of "canonical" is wildly different.  I can add
a patch to do those renames (I think doing an "opportunistic" rename would be a
bit much).