From: Jason Gunthorpe <jgg@nvidia.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>,
Marc Zyngier <maz@kernel.org>,
ankita@nvidia.com,
Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
oliver.upton@linux.dev, suzuki.poulose@arm.com,
yuzenghui@huawei.com, will@kernel.org, ardb@kernel.org,
akpm@linux-foundation.org, gshan@redhat.com, aniketa@nvidia.com,
cjia@nvidia.com, kwankhede@nvidia.com, targupta@nvidia.com,
vsethi@nvidia.com, acurrid@nvidia.com, apopple@nvidia.com,
jhubbard@nvidia.com, danw@nvidia.com, mochs@nvidia.com,
kvmarm@lists.linux.dev, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_* and NORMAL_NC for IO memory
Date: Wed, 6 Dec 2023 12:48:02 -0400 [thread overview]
Message-ID: <20231206164802.GT2692119@nvidia.com> (raw)
In-Reply-To: <ZXCf_e-ACqrj6VrV@arm.com>
On Wed, Dec 06, 2023 at 04:23:25PM +0000, Catalin Marinas wrote:
> On Wed, Dec 06, 2023 at 11:38:09AM -0400, Jason Gunthorpe wrote:
> > On Wed, Dec 06, 2023 at 04:18:05PM +0100, Lorenzo Pieralisi wrote:
> > > On Wed, Dec 06, 2023 at 11:05:56AM -0400, Jason Gunthorpe wrote:
> > > > On Wed, Dec 06, 2023 at 02:49:02PM +0000, Catalin Marinas wrote:
> > > > > BTW, on those Mellanox devices that require different attributes within
> > > > > a BAR, do they have a problem with speculative reads causing
> > > > > side-effects?
> > > >
> > > > Yes. We definitely have had that problem in the past on older
> > > > devices. VFIO must map the BAR using pgprot_device/noncached() into
> > > > the VMM, no other choice is functionally OK.
> > >
> > > Were those BARs tagged as prefetchable or non-prefetchable ? I assume the
> > > latter but please let me know if I am guessing wrong.
> >
> > I don't know it was quite old HW. Probably.
> >
> > Just because a BAR is not marked as prefetchable doesn't mean that the
> > device can't use NORMAL_NC on subsets of it.
>
> What about the other way around - would we have a prefetchable BAR that
> has portions which are unprefetchable?
I would say possibly.
Prefetch is a dead concept in PCIe, it was obsoleted in PCI-X about 20
years ago. No PCIe system has ever done prefetch.
There is a strong incentive to mark BAR's as prefetchable because it
allows 64 bit addressing in configurations with bridges.
So.. I would expect people have done interesting things here.
Jason
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next prev parent reply other threads:[~2023-12-06 16:48 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-05 3:30 [PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_* and NORMAL_NC for IO memory ankita
2023-12-05 9:21 ` Marc Zyngier
2023-12-05 11:40 ` Catalin Marinas
2023-12-05 13:05 ` Jason Gunthorpe
2023-12-05 14:37 ` Lorenzo Pieralisi
2023-12-05 14:44 ` Jason Gunthorpe
2023-12-05 16:24 ` Catalin Marinas
2023-12-05 17:10 ` Jason Gunthorpe
2023-12-05 16:22 ` Catalin Marinas
2023-12-05 16:43 ` Jason Gunthorpe
2023-12-05 17:01 ` Marc Zyngier
2023-12-05 17:33 ` Catalin Marinas
2023-12-05 17:50 ` Marc Zyngier
2023-12-05 18:40 ` Catalin Marinas
2023-12-06 11:39 ` Marc Zyngier
2023-12-06 12:14 ` Catalin Marinas
2023-12-06 15:16 ` Jason Gunthorpe
2023-12-06 16:31 ` Catalin Marinas
2023-12-06 17:20 ` Jason Gunthorpe
2023-12-06 18:58 ` Catalin Marinas
2023-12-06 19:03 ` Jason Gunthorpe
2023-12-06 19:06 ` Catalin Marinas
2023-12-07 2:53 ` Ankit Agrawal
2023-12-06 11:52 ` Lorenzo Pieralisi
2023-12-05 19:24 ` Catalin Marinas
2023-12-05 19:48 ` Jason Gunthorpe
2023-12-06 14:49 ` Catalin Marinas
2023-12-06 15:05 ` Jason Gunthorpe
2023-12-06 15:18 ` Lorenzo Pieralisi
2023-12-06 15:38 ` Jason Gunthorpe
2023-12-06 16:23 ` Catalin Marinas
2023-12-06 16:48 ` Jason Gunthorpe [this message]
2023-12-07 10:13 ` Lorenzo Pieralisi
2023-12-07 13:38 ` Jason Gunthorpe
2023-12-07 14:50 ` Lorenzo Pieralisi
2023-12-05 13:28 ` Lorenzo Pieralisi
2023-12-05 14:16 ` Shameerali Kolothum Thodi
2023-12-06 8:17 ` Shameerali Kolothum Thodi
2023-12-05 11:48 ` Catalin Marinas
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