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Subject: Re: [PATCH] drm/amdgpu: fix an underflow on non-4KB-page systems
From:   Xi Ruoyao <xry111@mengyan1223.wang>
To:     Christian =?ISO-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
        Dan =?ISO-8859-1?Q?Hor=E1k?= <dan@danny.cz>
Cc:     Christian =?ISO-8859-1?Q?K=F6nig?= 
        <ckoenig.leichtzumerken@gmail.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        David Airlie <airlied@linux.ie>,
        Felix Kuehling <Felix.Kuehling@amd.com>,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        amd-gfx@lists.freedesktop.org, Daniel Vetter <daniel@ffwll.ch>,
        stable@vger.kernel.org
Date:   Tue, 30 Mar 2021 23:46:58 +0800
In-Reply-To: <92dc0767-0c4e-34bc-d1ee-66105d0f2013@amd.com>
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On 2021-03-30 15:24 +0200, Christian König wrote:
> Am 30.03.21 um 15:23 schrieb Dan Horák:
> > On Tue, 30 Mar 2021 21:09:12 +0800
> > Xi Ruoyao <xry111@mengyan1223.wang> wrote:
> > 
> > > On 2021-03-30 21:02 +0800, Xi Ruoyao wrote:
> > > > On 2021-03-30 14:55 +0200, Christian König wrote:
> > > > > I rather see this as a kernel bug. Can you test if this code fragment
> > > > > fixes your issue:
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> > > > > b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> > > > > index 64beb3399604..e1260b517e1b 100644
> > > > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> > > > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> > > > > @@ -780,7 +780,7 @@ int amdgpu_info_ioctl(struct drm_device *dev, void
> > > > > *data, struct drm_file *filp)
> > > > >                   }
> > > > >                   dev_info->virtual_address_alignment =
> > > > > max((int)PAGE_SIZE, AMDGPU_GPU_PAGE_SIZE);
> > > > >                   dev_info->pte_fragment_size = (1 <<
> > > > > adev->vm_manager.fragment_size) * AMDGPU_GPU_PAGE_SIZE;
> > > > > -               dev_info->gart_page_size = AMDGPU_GPU_PAGE_SIZE;
> > > > > +               dev_info->gart_page_size =
> > > > > dev_info->virtual_address_alignment;
> > > > >                   dev_info->cu_active_number = adev-
> > > > > >gfx.cu_info.number;
> > > > >                   dev_info->cu_ao_mask = adev->gfx.cu_info.ao_cu_mask;
> > > > >                   dev_info->ce_ram_size = adev->gfx.ce_ram_size;
> > > > It works.  I've seen it at
> > > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fxen0n%2Flinux%2Fcommit%2F84ada72983838bd7ce54bc32f5d34ac5b5aae191&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7Cf37fddf20a8847edf67808d8f37ef23c%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637527074118791321%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=DZnmee38NGpiWRMX5LmlxOhxAzBMhAusnAWNnCxXTJ0%3D&amp;reserved=0
> > > > before (with a common sub-expression, though :).
> > > Some comment: on an old version of Fedora ported by Loongson, Xorg just
> > > hangs
> > > without this commit.  But on the system I built from source, I didn't see
> > > any
> > > issue before Linux 5.11.  So I misbelieved that it was something already
> > > fixed.
> > > 
> > > Dan: you can try it on your PPC 64 with non-4K page as well.
> > yup, looks good here as well, ppc64le (Power9) system with 64KB pages
> 
> Mhm, as far as I can say this patch never made it to us.

I think maybe its author considers it a "workaround" like me, as there is
already a "virtual_address_alignment" which seems correct.

> Can you please send it to the mailing list with me on CC?

I've sent it, together with my patch for using ~PAGE_MASK in parameter
validation.

-- 
Xi Ruoyao <xry111@mengyan1223.wang>
School of Aerospace Science and Technology, Xidian University