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Date: Fri, 10 Apr 2026 20:21:32 +0900
From: Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kwilczynski@kernel.org>
To: Ilpo =?utf-8?B?SsOkcnZpbmVu?= <ilpo.jarvinen@linux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>, Bjorn Helgaas <helgaas@kernel.org>,
	Manivannan Sadhasivam <mani@kernel.org>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Magnus Lindholm <linmag7@gmail.com>,
	Matt Turner <mattst88@gmail.com>,
	Richard Henderson <richard.henderson@linaro.org>,
	Christophe Leroy <chleroy@kernel.org>,
	Madhavan Srinivasan <maddy@linux.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Nicholas Piggin <npiggin@gmail.com>,
	Dexuan Cui <decui@microsoft.com>,
	Krzysztof =?utf-8?Q?Ha=C5=82asa?= <khalasa@piap.pl>,
	Lukas Wunner <lukas@wunner.de>,
	Oliver O'Halloran <oohall@gmail.com>,
	Saurabh Singh Sengar <ssengar@microsoft.com>,
	Shuan He <heshuan@bytedance.com>,
	Srivatsa Bhat <srivatsabhat@microsoft.com>,
	linux-pci@vger.kernel.org, linux-alpha@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 13/20] alpha/PCI: Clean up __pci_mmap_fits()
Message-ID: <20260410112132.GA1756033@rocinante>
References: <20260410055040.39233-1-kwilczynski@kernel.org>
 <20260410055040.39233-14-kwilczynski@kernel.org>
 <66eb23bf-1995-363f-78e6-f5a397a063a2@linux.intel.com>
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In-Reply-To: <66eb23bf-1995-363f-78e6-f5a397a063a2@linux.intel.com>

Hello,

> > Currently, __pci_mmap_fits() computes the BAR size using
> > pci_resource_len() - 1, which wraps to a large value when the
> > BAR length is zero, causing the bounds check to incorrectly
> > succeed.
> > 
> > Thus, add an early return for empty resources.
> > 
> > Also, remove the WARN() that fires when userspace attempts to
> > mmap beyond the BAR bounds.  The check still returns 0 to reject
> > the mapping, but the warning is excessive for normal operation.
> > 
> > A similar warning was removed from the PCI core in the commit
> > 3b519e4ea618 ("PCI: fix size checks for mmap() on /proc/bus/pci files").
> 
> This looks like entirely separate two changes to me which just happen 
> within the same context.

True.  I could split this into two separate patches.  However, the early
return is so trivial, that I decided to keep it here, in lieu of that the
linked patch did, too.

Thoughts?

Thank you!

	Krzysztof