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Fri, 21 Aug 2026 06:27:09 -0700 (PDT) Message-ID: <12442106-e756-4902-b9fd-c760da04f849@gmail.com> Date: Fri, 21 Aug 2026 14:27:08 +0100 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 2/5] KVM: arm64: Add pre_fault_memory implementation To: Alexandru Elisei 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 References: <20260612162354.73378-1-jackabt.amazon@gmail.com> <20260612162354.73378-3-jackabt.amazon@gmail.com> Content-Language: en-US From: "Thomson, Jack" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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