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From: Marc Zyngier <maz@kernel.org>
To: <ankita@nvidia.com>
Cc: <jgg@nvidia.com>, <alex.williamson@redhat.com>,
	<naoya.horiguchi@nec.com>, <oliver.upton@linux.dev>,
	<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>,
	<kvm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>, <linux-mm@kvack.org>
Subject: Re: [PATCH v3 0/6] Expose GPU memory as coherently CPU accessible
Date: Wed, 12 Apr 2023 13:28:08 +0100	[thread overview]
Message-ID: <86sfd5l1yf.wl-maz@kernel.org> (raw)
In-Reply-To: <20230405180134.16932-1-ankita@nvidia.com>

On Wed, 05 Apr 2023 19:01:28 +0100,
<ankita@nvidia.com> wrote:
> 
> From: Ankit Agrawal <ankita@nvidia.com>
> 
> NVIDIA's upcoming Grace Hopper Superchip provides a PCI-like device
> for the on-chip GPU that is the logical OS representation of the
> internal propritary cache coherent interconnect.
> 
> This representation has a number of limitations compared to a real PCI
> device, in particular, it does not model the coherent GPU memory
> aperture as a PCI config space BAR, and PCI doesn't know anything
> about cacheable memory types.
> 
> Provide a VFIO PCI variant driver that adapts the unique PCI
> representation into a more standard PCI representation facing
> userspace. The GPU memory aperture is obtained from ACPI, according to
> the FW specification, and exported to userspace as the VFIO_REGION
> that covers the first PCI BAR. qemu will naturally generate a PCI
> device in the VM where the cacheable aperture is reported in BAR1.
> 
> Since this memory region is actually cache coherent with the CPU, the
> VFIO variant driver will mmap it into VMA using a cacheable mapping.
> 
> As this is the first time an ARM environment has placed cacheable
> non-struct page backed memory (eg from remap_pfn_range) into a KVM
> page table, fix a bug in ARM KVM where it does not copy the cacheable
> memory attributes from non-struct page backed PTEs to ensure the guest
> also gets a cacheable mapping.

This is not a bug, but a conscious design decision. As you pointed out
above, nothing needed this until now, and a device mapping is the only
safe thing to do as we know exactly *nothing* about the memory that
gets mapped.

	M.

-- 
Without deviation from the norm, progress is not possible.

  parent reply	other threads:[~2023-04-12 12:28 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-04-05 18:01 [PATCH v3 0/6] Expose GPU memory as coherently CPU accessible ankita
2023-04-05 18:01 ` [PATCH v3 1/6] kvm: determine memory type from VMA ankita
2023-04-12 12:43   ` Marc Zyngier
2023-04-12 13:01     ` Jason Gunthorpe
2023-05-31 11:35       ` Catalin Marinas
2023-06-14 12:44         ` Jason Gunthorpe
2023-07-14  8:10         ` Benjamin Herrenschmidt
2023-07-16 15:09           ` Catalin Marinas
2023-07-16 22:30             ` Jason Gunthorpe
2023-07-17 18:35               ` Alex Williamson
2023-07-25  6:18                 ` Benjamin Herrenschmidt
2023-04-05 18:01 ` [PATCH v3 2/6] vfio/nvgpu: expose GPU device memory as BAR1 ankita
2023-04-05 21:07   ` kernel test robot
2023-04-05 18:01 ` [PATCH v3 3/6] mm: handle poisoning of pfn without struct pages ankita
2023-04-05 21:07   ` kernel test robot
2023-05-09  9:51   ` HORIGUCHI NAOYA(堀口　直也)
2023-05-15 11:18     ` Ankit Agrawal
2023-05-23  5:43       ` HORIGUCHI NAOYA(堀口　直也)
2023-04-05 18:01 ` [PATCH v3 4/6] mm: Add poison error check in fixup_user_fault() for mapped PFN ankita
2023-04-05 18:01 ` [PATCH v3 5/6] mm: Change ghes code to allow poison of non-struct PFN ankita
2023-04-05 18:01 ` [PATCH v3 6/6] vfio/nvgpu: register device memory for poison handling ankita
2023-04-05 20:24   ` Zhi Wang
2023-04-05 21:50   ` kernel test robot
2023-05-24  9:53   ` Dan Carpenter
2023-04-06 12:07 ` [PATCH v3 0/6] Expose GPU memory as coherently CPU accessible David Hildenbrand
2023-04-12  8:43   ` Ankit Agrawal
2023-04-12  9:48     ` Marc Zyngier
2023-04-12 12:28 ` Marc Zyngier [this message]
2023-04-12 12:53   ` Jason Gunthorpe
2023-04-13  9:52     ` Marc Zyngier
2023-04-13 13:19       ` Jason Gunthorpe

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