linux-kernel - Re: [PATCH] nvme-pci: Make nvme_pci_npages_prp() __always

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Message-ID: <20250507065913.GA31959@lst.de>
Date: Wed, 7 May 2025 08:59:13 +0200
From: Christoph Hellwig <hch@....de>
To: Kees Cook <kees@...nel.org>
Cc: Christoph Hellwig <hch@....de>, Keith Busch <kbusch@...nel.org>,
	kernel test robot <lkp@...el.com>, Jens Axboe <axboe@...nel.dk>,
	Sagi Grimberg <sagi@...mberg.me>, linux-nvme@...ts.infradead.org,
	Chaitanya Kulkarni <kch@...dia.com>, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] nvme-pci: Make nvme_pci_npages_prp() __always_inline

On Tue, May 06, 2025 at 10:55:31PM -0700, Kees Cook wrote:
> On Wed, May 07, 2025 at 06:47:54AM +0200, Christoph Hellwig wrote:
> > On Tue, May 06, 2025 at 08:35:40PM -0700, Kees Cook wrote:
> > > The only reason nvme_pci_npages_prp() could be used as a compile-time
> > > known result in BUILD_BUG_ON() is because the compiler was always choosing
> > > to inline the function. Under special circumstances (sanitizer coverage
> > > functions disabled for __init functions on ARCH=um), the compiler decided
> > > to stop inlining it:
> > 
> > Can we place just fix um to still force inlining inline functions instead
> > of needing these workarounds?
> 
> Oh, I don't have the history here. Is there something about UM and
> forcing off inlining?

Maybe I'm misunderstandng your report, but what causes the failure
to inline?