From: "Thomson, Jack" <jackabt.amazon@gmail.com>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: maz@kernel.org, oupton@kernel.org, pbonzini@redhat.com,
joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com,
yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org,
shuah@kernel.org, corbet@lwn.net, vladimir.murzin@arm.com,
linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org,
isaku.yamahata@intel.com, Jack Thomson <jackabt@amazon.com>
Subject: Re: [PATCH v5 2/5] KVM: arm64: Add pre_fault_memory implementation
Date: Fri, 21 Aug 2026 14:27:08 +0100 [thread overview]
Message-ID: <12442106-e756-4902-b9fd-c760da04f849@gmail.com> (raw)
In-Reply-To: <alEXGmKiXgWPPdhF@raptor>
Hi Alex,
On 10/07/2026 5:00 pm, Alexandru Elisei wrote:
>> Does it guarantee that, after it completes and returns to userspace, the
>> address range [gpa, gpa + size] is mapped in the VM's stage 2 tables? Or
>> does it guarantee that the address range was mapped at stage 2 at some
>> point during the ioctl's execution, but parts, or all of it, might not be
>> mapped after the ioctl completes and returns to userspace?
>
> Nevermind, spend some time thinking about it and it turns out it's
> impossible for KVM to guarantee that the memory is still mapped after the
> ioctls returns. So I answered my own question, thanks.
>
> Alex
>
Yeah it's best effort, as if a vCPU had faulted the range itself. This
could be undone by an invalidation or memslot update. The value is in
the common cast (for us, post-copy migration) the guest doesn't pay the
stage-2 fault fault cost at run time.
I think it would be worth me adding a sentence to the documentation
noting there is no persistance guarentee.
--
Thanks,
Jack
next prev parent reply other threads:[~2026-08-21 13:27 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-12 16:23 [PATCH v5 0/5] KVM: arm64: Add KVM_PRE_FAULT_MEMORY support Jack Thomson
2026-06-12 16:23 ` [PATCH v5 1/5] KVM: arm64: Pass walk flags to kvm_pgtable_get_leaf() Jack Thomson
2026-06-12 16:23 ` [PATCH v5 2/5] KVM: arm64: Add pre_fault_memory implementation Jack Thomson
2026-07-08 15:25 ` Alexandru Elisei
2026-07-10 16:00 ` Alexandru Elisei
2026-08-21 13:27 ` Thomson, Jack [this message]
2026-07-10 16:03 ` Alexandru Elisei
2026-08-03 6:06 ` Aneesh Kumar K.V
2026-08-11 16:03 ` Alexandru Elisei
2026-08-21 14:05 ` Thomson, Jack
2026-08-21 13:52 ` Thomson, Jack
2026-08-25 12:29 ` Alexandru Elisei
2026-08-25 13:04 ` Thomson, Jack
2026-07-27 11:11 ` Vincent Donnefort
2026-08-21 14:01 ` Thomson, Jack
2026-06-12 16:23 ` [PATCH v5 3/5] KVM: selftests: Enable pre_fault_memory_test for arm64 Jack Thomson
2026-06-12 16:23 ` [PATCH v5 4/5] KVM: selftests: Add option for different backing in pre-fault tests Jack Thomson
2026-06-12 16:23 ` [PATCH v5 5/5] KVM: selftests: Add nested pre-fault test for arm64 Jack Thomson
2026-06-12 16:35 ` sashiko-bot
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