linux-kernel - Re: [PATCH v4] x86/hyperv: Fix kdump on Azure CVMs

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Message-ID: <aLoeQXAo5PMDA5hn@liuwe-devbox-ubuntu-v2.lamzopl0uupeniq2etz1fddiyg.xx.internal.cloudapp.net>
Date: Thu, 4 Sep 2025 23:18:25 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: linux-hyperv@...r.kernel.org, Michael Kelley <mhklinux@...look.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
	Tianyu Lan <tiala@...rosoft.com>, Li Tian <litian@...hat.com>,
	Philipp Rudo <prudo@...hat.com>
Subject: Re: [PATCH v4] x86/hyperv: Fix kdump on Azure CVMs

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 <vkuznets@...hat.com>

No fixes tag for this one?

Should it be marked as a stable backport?

Thanks,
Wei