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

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Message-ID: <aKeeRynpwFTSONfm@linux.dev>
Date: Thu, 21 Aug 2025 15:31:52 -0700
From: Oliver Upton <oliver.upton@...ux.dev>
To: Sean Christopherson <seanjc@...gle.com>
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

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.

> +	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.

Thanks,
Oliver