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Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , x86@kernel.org, linux-kernel@vger.kernel.org, Nuno Das Neves , Tianyu Lan , Li Tian , Philipp Rudo Subject: Re: [PATCH v4] x86/hyperv: Fix kdump on Azure CVMs In-Reply-To: References: <20250828091618.884950-1-vkuznets@redhat.com> Date: Fri, 05 Sep 2025 10:48:22 +0300 Message-ID: <87frd1figp.fsf@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Wei Liu writes: > On Thu, Aug 28, 2025 at 12:16:18PM +0300, Vitaly Kuznetsov wrote: >> Azure CVM instance types featuring a paravisor hang upon kdump. The >> investigation shows that makedumpfile causes a hang when it steps on a page >> which was previously share with the host >> (HVCALL_MODIFY_SPARSE_GPA_PAGE_HOST_VISIBILITY). The new kernel has no >> knowledge of these 'special' regions (which are Vmbus connection pages, >> GPADL buffers, ...). There are several ways to approach the issue: >> - Convey the knowledge about these regions to the new kernel somehow. >> - Unshare these regions before accessing in the new kernel (it is unclear >> if there's a way to query the status for a given GPA range). >> - Unshare these regions before jumping to the new kernel (which this patch >> implements). >> >> To make the procedure as robust as possible, store PFN ranges of shared >> regions in a linked list instead of storing GVAs and re-using >> hv_vtom_set_host_visibility(). This also allows to avoid memory allocation >> on the kdump/kexec path. >> >> Signed-off-by: Vitaly Kuznetsov > > No fixes tag for this one? > Personally, I don't see this as a 'bug', it's rather a missing feature. In theory, we can add something like Fixes: 810a52126502 ("x86/hyperv: Add new hvcall guest address host visibility support") but I'm on the fence whether this is accurate or not. > Should it be marked as a stable backport? I think it may make sense even without an explicit 'Fixes:': kdump is the user's last resort when it comes to kernel crashes and doubly so on CVMs. Pure kexec may also come handy. -- Vitaly