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From: Oliver Upton <oliver.upton@linux.dev>
To: Jack Thomson <jackabt.amazon@gmail.com>
Cc: maz@kernel.org, pbonzini@redhat.com, joey.gouly@arm.com,
	suzuki.poulose@arm.com, yuzenghui@huawei.com,
	catalin.marinas@arm.com, will@kernel.org, shuah@kernel.org,
	linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	isaku.yamahata@intel.com, roypat@amazon.co.uk,
	kalyazin@amazon.co.uk, jackabt@amazon.com
Subject: Re: [PATCH 0/6] KVM ARM64 pre_fault_memory
Date: Thu, 11 Sep 2025 11:56:43 -0700	[thread overview]
Message-ID: <aMMba1r3AVdC9cQw@linux.dev> (raw)
In-Reply-To: <20250911134648.58945-1-jackabt.amazon@gmail.com>

Hi Jack,

On Thu, Sep 11, 2025 at 02:46:42PM +0100, Jack Thomson wrote:
> From: Jack Thomson <jackabt@amazon.com>
> 
> Overview:
> 
> This patch series adds ARM64 support for the KVM_PRE_FAULT_MEMORY
> feature, which was previously only available on x86 [1]. This allows
> a reduction in the number of stage-2 faults during execution. This is
> beneficial in post-copy migration scenarios, particularly in memory
> intensive applications, where high latencies are experienced due to
> the stage-2 faults when pre-populating memory via UFFD / memcpy.

Thanks for posting the series. More of a general comment on the UAPI
documentation:

  "... However, KVM does not mark any newly created stage-2 PTE as Accessed."

This behavior is x86-specific since kvm_pgtable_stage2_map() will lay
down PTEs with the AF set. Probably shouldn't have documented the
internal state of the stage-2 in the first place but oh well, please
just update the UAPI description to make it clear this is x86-specific.

Thanks
Oliver


      parent reply	other threads:[~2025-09-11 18:57 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-09-11 13:46 [PATCH 0/6] KVM ARM64 pre_fault_memory Jack Thomson
2025-09-11 13:46 ` [PATCH 1/6] KVM: arm64: Add __gmem_abort and __user_mem_abort Jack Thomson
2025-09-11 18:27   ` Oliver Upton
2025-09-11 13:46 ` [PATCH 2/6] KVM: arm64: Add KVM_PGTABLE_WALK_PRE_FAULT walk flag Jack Thomson
2025-09-11 13:46 ` [PATCH 3/6] KVM: arm64: Add pre_fault_memory implementation Jack Thomson
2025-09-11 18:42   ` Oliver Upton
2025-09-29 13:59     ` Thomson, Jack
2025-09-30  0:53       ` Oliver Upton
2025-09-11 13:46 ` [PATCH 4/6] KVM: selftests: Fix unaligned mmap allocations Jack Thomson
2025-09-11 13:46 ` [PATCH 5/6] KVM: selftests: Enable pre_fault_memory_test for arm64 Jack Thomson
2025-09-11 13:46 ` [PATCH 6/6] KVM: selftests: Add option for different backing in pre-fault tests Jack Thomson
2025-09-11 18:56 ` Oliver Upton [this message]

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