RE: [PATCH v7 6/6] vfio/nvgrace-gpu: wait for the GPU mem to be ready

[Shameer Kolothum]

> -----Original Message-----
> From: Ankit Agrawal <ankita@xxxxxxxxxx>
> Sent: 26 November 2025 05:26
> To: Ankit Agrawal <ankita@xxxxxxxxxx>; jgg@xxxxxxxx; Yishai Hadas
> <yishaih@xxxxxxxxxx>; Shameer Kolothum <skolothumtho@xxxxxxxxxx>;
> kevin.tian@xxxxxxxxx; alex@xxxxxxxxxxx; Aniket Agashe
> <aniketa@xxxxxxxxxx>; Vikram Sethi <vsethi@xxxxxxxxxx>; Matt Ochs
> <mochs@xxxxxxxxxx>
> Cc: Yunxiang.Li@xxxxxxx; yi.l.liu@xxxxxxxxx;
> zhangdongdong@xxxxxxxxxxxxxxxxxx; Avihai Horon <avihaih@xxxxxxxxxx>;
> bhelgaas@xxxxxxxxxx; peterx@xxxxxxxxxx; pstanner@xxxxxxxxxx; Alistair
> Popple <apopple@xxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; Neo Jia <cjia@xxxxxxxxxx>; Kirti Wankhede
> <kwankhede@xxxxxxxxxx>; Tarun Gupta (SW-GPU) <targupta@xxxxxxxxxx>;
> Zhi Wang <zhiw@xxxxxxxxxx>; Dan Williams <danw@xxxxxxxxxx>; Dheeraj
> Nigam <dnigam@xxxxxxxxxx>; Krishnakant Jaju <kjaju@xxxxxxxxxx>
> Subject: [PATCH v7 6/6] vfio/nvgrace-gpu: wait for the GPU mem to be ready
> 
> From: Ankit Agrawal <ankita@xxxxxxxxxx>
> 
> Speculative prefetches from CPU to GPU memory until the GPU is
> ready after reset can cause harmless corrected RAS events to
> be logged on Grace systems. It is thus preferred that the
> mapping not be re-established until the GPU is ready post reset.
> 
> The GPU readiness can be checked through BAR0 registers similar
> to the checking at the time of device probe.
> 
> 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 or read/write access which amortizes the GPU readiness
> time.
> 
> The first fault and read/write checks the GPU state when the
> reset_done flag - which denotes whether the GPU has just been
> reset. The memory_lock is taken across map/access to avoid
> races with GPU reset.
> 
> Cc: Shameer Kolothum <skolothumtho@xxxxxxxxxx>
> Cc: Alex Williamson <alex@xxxxxxxxxxx>
> Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> Cc: Vikram Sethi <vsethi@xxxxxxxxxx>
> Suggested-by: Alex Williamson <alex@xxxxxxxxxxx>
> Signed-off-by: Ankit Agrawal <ankita@xxxxxxxxxx>
> ---
>  drivers/vfio/pci/nvgrace-gpu/main.c | 81 +++++++++++++++++++++++++---
> -
>  1 file changed, 72 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/vfio/pci/nvgrace-gpu/main.c b/drivers/vfio/pci/nvgrace-
> gpu/main.c
> index b46984e76be7..3064f8aca858 100644
> --- a/drivers/vfio/pci/nvgrace-gpu/main.c
> +++ b/drivers/vfio/pci/nvgrace-gpu/main.c
> @@ -104,6 +104,17 @@ static int nvgrace_gpu_open_device(struct
> vfio_device *core_vdev)
>  		mutex_init(&nvdev->remap_lock);
>  	}
> 
> +	/*
> +	 * GPU readiness is checked by reading the BAR0 registers.
> +	 *
> +	 * ioremap BAR0 to ensure that the BAR0 mapping is present before
> +	 * register reads on first fault before establishing any GPU
> +	 * memory mapping.
> +	 */
> +	ret = vfio_pci_core_setup_barmap(vdev, 0);
> +	if (ret)
> +		return ret;

Should make sure vfio_pci_core_disable() is called on err path above.

With that,
Reviewed-by: Shameer Kolothum <skolothumtho@xxxxxxxxxx>