From: Catalin Marinas <catalin.marinas@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Vikram Sethi <vsethi@nvidia.com>,
Alex Williamson <alex.williamson@redhat.com>,
Mark Kettenis <mark.kettenis@xs4all.nl>,
Marc Zyngier <maz@kernel.org>,
Shanker Donthineni <sdonthineni@nvidia.com>,
"christoffer.dall@arm.com" <christoffer.dall@arm.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
Jason Sequeira <jsequeira@nvidia.com>
Subject: Re: [RFC 1/2] vfio/pci: keep the prefetchable attribute of a BAR region in VMA
Date: Wed, 5 May 2021 19:02:31 +0100 [thread overview]
Message-ID: <20210505180228.GA3874@arm.com> (raw)
In-Reply-To: <20210504083005.GA12290@willie-the-truck>
On Tue, May 04, 2021 at 09:30:05AM +0100, Will Deacon wrote:
> On Mon, May 03, 2021 at 10:03:59PM +0000, Vikram Sethi wrote:
> > Will/Catalin, perhaps you could explain your thought process on why you chose
> > Normal NC for ioremap_wc on the armv8 linux port instead of Device GRE or other
> > Device Gxx.
>
> I think a combination of: compatibility with 32-bit Arm, the need to
> support unaligned accesses and the potential for higher performance.
IIRC the _wc suffix also matches the pgprot_writecombine() used by some
drivers to map a video framebuffer into user space. Accesses to the
framebuffer are not guaranteed to be aligned (memset/memcpy don't ensure
alignment on arm64 and the user doesn't have a memset_io or memcpy_toio).
> Furthermore, ioremap() already gives you a Device memory type, and we're
> tight on MAIR space.
We have MT_DEVICE_GRE currently reserved though no in-kernel user, we
might as well remove it.
--
Catalin
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next prev parent reply other threads:[~2021-05-05 18:04 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-29 16:29 [RFC 0/2] [RFC] Honor PCI prefetchable attributes for a virtual machine on ARM64 Shanker Donthineni
2021-04-29 16:29 ` [RFC 1/2] vfio/pci: keep the prefetchable attribute of a BAR region in VMA Shanker Donthineni
2021-04-29 18:28 ` Alex Williamson
2021-04-29 19:14 ` Shanker R Donthineni
2021-04-29 19:46 ` Alex Williamson
2021-04-29 22:08 ` Vikram Sethi
2021-04-30 11:25 ` Shanker R Donthineni
2021-04-30 11:47 ` Marc Zyngier
2021-04-30 13:07 ` Shanker R Donthineni
2021-04-30 15:07 ` Marc Zyngier
2021-04-30 14:58 ` Shanker R Donthineni
2021-04-30 15:31 ` Marc Zyngier
2021-04-30 16:57 ` Vikram Sethi
2021-05-01 9:30 ` Marc Zyngier
2021-05-01 11:36 ` Shanker R Donthineni
2021-05-03 9:50 ` Marc Zyngier
2021-05-03 12:08 ` Shanker R Donthineni
2021-05-02 17:56 ` Vikram Sethi
2021-05-03 10:17 ` Marc Zyngier
2021-05-03 13:35 ` Mark Kettenis
2021-05-03 13:59 ` Vikram Sethi
2021-05-03 14:44 ` Alex Williamson
2021-05-03 22:03 ` Vikram Sethi
2021-05-04 8:30 ` Will Deacon
2021-05-05 18:02 ` Catalin Marinas [this message]
2021-05-06 7:22 ` Christoph Hellwig
2021-05-08 16:33 ` Shanker R Donthineni
2021-06-02 9:37 ` Marc Zyngier
2021-05-04 18:03 ` Alex Williamson
2021-06-02 9:11 ` Marc Zyngier
2021-04-30 9:54 ` Lorenzo Pieralisi
2021-04-30 12:38 ` Jason Gunthorpe
2021-04-29 16:29 ` [RFC 2/2] KVM: arm64: Add write-combine support for stage-2 entries Shanker Donthineni
2021-05-03 7:01 ` [RFC 0/2] [RFC] Honor PCI prefetchable attributes for a virtual machine on ARM64 Christoph Hellwig
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