linux-kernel - Re: [PATCH v9 0/6] vfio/nvgrace-gpu: Support huge PFNMAP and wait for GPU ready post reset

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Message-ID: <20251128124439.3a30cf93.alex@shazbot.org>
Date: Fri, 28 Nov 2025 12:44:39 -0700
From: Alex Williamson <alex@...zbot.org>
To: <ankita@...dia.com>
Cc: <jgg@...pe.ca>, <yishaih@...dia.com>, <skolothumtho@...dia.com>,
 <kevin.tian@...el.com>, <aniketa@...dia.com>, <vsethi@...dia.com>,
 <mochs@...dia.com>, <Yunxiang.Li@....com>, <yi.l.liu@...el.com>,
 <zhangdongdong@...incomputing.com>, <avihaih@...dia.com>,
 <bhelgaas@...gle.com>, <peterx@...hat.com>, <pstanner@...hat.com>,
 <apopple@...dia.com>, <kvm@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <cjia@...dia.com>, <kwankhede@...dia.com>,
 <targupta@...dia.com>, <zhiw@...dia.com>, <danw@...dia.com>,
 <dnigam@...dia.com>, <kjaju@...dia.com>
Subject: Re: [PATCH v9 0/6] vfio/nvgrace-gpu: Support huge PFNMAP and wait
 for GPU ready post reset

On Thu, 27 Nov 2025 17:06:26 +0000
<ankita@...dia.com> wrote:

> From: Ankit Agrawal <ankita@...dia.com>
> 
> NVIDIA's Grace based system have large GPU device memory. The device
> memory is mapped as VM_PFNMAP in the VMM VMA. The nvgrace-gpu
> module could make use of the huge PFNMAP support added in mm [1].
> 
> To achieve this, nvgrace-gpu module is updated to implement huge_fault ops.
> The implementation establishes mapping according to the order request.
> Note that if the PFN or the VMA address is unaligned to the order, the
> mapping fallbacks to the PTE level.
> 
> Secondly, it is expected that the mapping not be re-established until
> the GPU is ready post reset. Presence of the mappings during that time
> could potentially leads to harmless corrected RAS events to be logged if
> the CPU attempts to do speculative reads on the GPU memory on the Grace
> systems.
> 
> It can take several seconds for the GPU to be ready. So it is desirable
> that the time overlaps as much of the VM startup as possible to reduce
> impact on the VM bootup time. The GPU readiness state is thus checked
> on the first fault/huge_fault request which amortizes the GPU readiness
> time. The GPU readiness is checked through BAR0 registers as is done
> at the device probe.
> 
> Patch 1 Refactor vfio_pci_mmap_huge_fault and export the code to map
> at the various levels.
> 
> Patch 2 implements support for huge pfnmap.
> 
> Patch 3 vfio_pci_core_mmap cleanup.
> 
> Patch 4 split the code to check the device readiness.
> 
> Patch 5 reset_done handler implementation
> 
> Patch 6 Ensures that the GPU is ready before re-establishing the mapping
> after reset.
> 
> Applied over 6.18-rc6.
> 
> Link: https://lore.kernel.org/all/20240826204353.2228736-1-peterx@redhat.com/ [1]
> 
> Changelog:
> [v9]

Applied to vfio next branch for v6.19.  Thanks,

Alex