Re: [PATCH] drm/amdgpu: ensure no_hw_access is visible before MMIO

["Lazar, Lijo" <lijo.lazar@amd.com>]

On 28-Jan-26 11:53 AM, Perry Yuan wrote:
> Add a full memory barrier after clearing no_hw_access in
> amdgpu_device_mode1_reset() so subsequent PCI state restore
> access cannot observe stale state on other CPUs.
> 

Just want to reiterate that this approach masks the original logical 
errors within amdgpu.

For ex: this is one such which would not have been caught in the first 
place with shortcuts like these.

12caf3b76150 drm/amdkfd: Handle GPU reset and drain retry fault race

Thanks,
Lijo

> Fixes: 91ae0045130b ("drm/amd/pm: Disable MMIO access during SMU Mode 1 reset")
> Signed-off-by: Perry Yuan <perry.yuan@amd.com>
> Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> index b2deb6a74eb2..e69ab8a923e3 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> @@ -5735,6 +5735,9 @@ int amdgpu_device_mode1_reset(struct amdgpu_device *adev)
>   	/* enable mmio access after mode 1 reset completed */
>   	adev->no_hw_access = false;
>   
> +	/* ensure no_hw_access is updated before we access hw */
> +	smp_mb();
> +
>   	amdgpu_device_load_pci_state(adev->pdev);
>   	ret = amdgpu_psp_wait_for_bootloader(adev);
>   	if (ret)