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Date: Tue, 14 Apr 2026 04:44:51 +0000
From: Wei Liu <wei.liu@kernel.org>
To: Michael Kelley <mhklinux@outlook.com>
Cc: Naman Jain <namjain@linux.microsoft.com>,
	"K . Y . Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
	Long Li <longli@microsoft.com>,
	Saurabh Sengar <ssengar@linux.microsoft.com>,
	"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] mshv_vtl: Fix vmemmap_shift exceeding MAX_FOLIO_ORDER
Message-ID: <20260414044451.GC2787213@liuwe-devbox-debian-v2.local>
References: <20260406092459.2351028-1-namjain@linux.microsoft.com>
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On Mon, Apr 06, 2026 at 02:08:07PM +0000, Michael Kelley wrote:
> From: Naman Jain <namjain@linux.microsoft.com> Sent: Monday, April 6, 2026 2:25 AM
> > 
> > When registering VTL0 memory via MSHV_ADD_VTL0_MEMORY, the kernel
> > computes pgmap->vmemmap_shift as the number of trailing zeros in the
> > OR of start_pfn and last_pfn, intending to use the largest compound
> > page order both endpoints are aligned to.
> > 
> > However, this value is not clamped to MAX_FOLIO_ORDER, so a
> > sufficiently aligned range (e.g. physical range
> > [0x800000000000, 0x800080000000), corresponding to start_pfn=0x800000000
> > with 35 trailing zeros) can produce a shift larger than what
> > memremap_pages() accepts, triggering a WARN and returning -EINVAL:
> > 
> >   WARNING: ... memremap_pages+0x512/0x650
> >   requested folio size unsupported
> > 
> > The MAX_FOLIO_ORDER check was added by
> > commit 646b67d57589 ("mm/memremap: reject unreasonable folio/compound
> > page sizes in memremap_pages()").
> > 
> > Fix this by clamping vmemmap_shift to MAX_FOLIO_ORDER so we always
> > request the largest order the kernel supports, in those cases, rather
> > than an out-of-range value.
> > 
> > Also fix the error path to propagate the actual error code from
> > devm_memremap_pages() instead of hard-coding -EFAULT, which was
> > masking the real -EINVAL return.
> > 
> > Fixes: 7bfe3b8ea6e3 ("Drivers: hv: Introduce mshv_vtl driver")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Naman Jain <namjain@linux.microsoft.com>

Applied. Thanks.