From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Veronika kabatova <vkabatov@redhat.com>,
Robin Murphy <robin.murphy@arm.com>,
Will Deacon <will@kernel.org>, Hanjun Guo <guohanjun@huawei.com>,
Sudeep Holla <sudeep.holla@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>
Subject: Re: [PATCH v2 1/3] ACPI: osl: Add __force attribute in acpi_os_map_iomem() cast
Date: Wed, 11 Aug 2021 15:01:57 +0100 [thread overview]
Message-ID: <20210811140157.GA28658@e123427-lin.cambridge.arm.com> (raw)
In-Reply-To: <CAMj1kXEB1CFj1svCWu7yOoUi_OkEqYEUQnB_XWOd3gD+ejO_6w@mail.gmail.com>
On Wed, Aug 11, 2021 at 12:40:28PM +0200, Ard Biesheuvel wrote:
> On Tue, 10 Aug 2021 at 18:46, Christoph Hellwig <hch@infradead.org> wrote:
> >
> > On Mon, Aug 02, 2021 at 04:23:57PM +0100, Lorenzo Pieralisi wrote:
> > > Add a __force attribute to the void* cast in acpi_os_map_iomem()
> > > to prevent sparse warnings.
> >
> > Err, no. These annotation are there for a reason and need to
> > be propagated instead. And independent of that a __force cast
> > without a comment explaining it is a complete no-go.
>
> The whole problem we are solving here is that ACPI, being based on
> x86, conflates MMIO mappings with memory mappings, and has been using
> the same underlying infrastructure for either. On arm64, this is not
> sufficient, given that the semantics of uncached memory vs device are
> different (the former permits unaligned accesses and clear cacheline
> instructions, but the latter doesn't). A recent optimization applied
> to memcpy() on arm64 (which now relies more on unaligned accesses for
> performance) has uncovered an issue where firmware tables being mapped
> non-cacheable by the ACPI core will end up using device mappings,
> which causes memcpy() to choke on their contents.
>
> So propagating the annotation makes no sense, as we are creating a
> memory mapping using the iomem primitive. I wouldn't object to a
> comment being added, but I think the context should have been obvious
> to anyone who had bothered to look at the entire series.
I can add a comment and respin. Basically a __force attribute is
added to ignore a sparse warning that's been ignored for aeons
anyway - I will add the rationale above.
drivers/acpi/osl.c:379:17: warning: cast removes address space '__iomem' of expression
next prev parent reply other threads:[~2021-08-11 14:02 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-26 10:00 [PATCH] ACPI: Add memory semantics to acpi_os_map_memory() Lorenzo Pieralisi
2021-07-26 15:55 ` Ard Biesheuvel
2021-07-27 10:06 ` Lorenzo Pieralisi
2021-07-27 10:09 ` Ard Biesheuvel
2021-07-27 16:38 ` Lorenzo Pieralisi
2021-07-27 4:21 ` Hanjun Guo
2021-08-02 15:23 ` [PATCH v2 0/3] ACPI: Fix acpi_os_map_memory() memory semantics Lorenzo Pieralisi
2021-08-02 15:37 ` Ard Biesheuvel
2021-08-23 10:35 ` [PATCH v3] ACPI: Add memory semantics to acpi_os_map_memory() Lorenzo Pieralisi
2021-08-23 10:46 ` [PATCH RESEND " Lorenzo Pieralisi
2021-08-23 12:30 ` Catalin Marinas
2021-08-25 17:46 ` Rafael J. Wysocki
2021-08-02 15:23 ` [PATCH v2 1/3] ACPI: osl: Add __force attribute in acpi_os_map_iomem() cast Lorenzo Pieralisi
2021-08-10 16:45 ` Christoph Hellwig
2021-08-11 10:40 ` Ard Biesheuvel
2021-08-11 14:01 ` Lorenzo Pieralisi [this message]
2021-08-11 14:08 ` Christoph Hellwig
2021-08-11 14:55 ` Lorenzo Pieralisi
2021-08-16 9:58 ` Lorenzo Pieralisi
2021-08-16 10:21 ` Ard Biesheuvel
2021-08-16 10:59 ` Robin Murphy
2021-08-16 13:57 ` Rafael J. Wysocki
2021-08-02 15:23 ` [PATCH v2 2/3] ACPI: osl: Reorder acpi_os_map_iomem() __ref annotation Lorenzo Pieralisi
2021-08-02 15:23 ` [PATCH v2 3/3] ACPI: Add memory semantics to acpi_os_map_memory() Lorenzo Pieralisi
2021-08-02 16:46 ` Catalin Marinas
2021-08-03 9:16 ` Lorenzo Pieralisi
2021-08-05 19:02 ` Rafael J. Wysocki
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