Re: Screen corruption using radeon kernel driver

[Mikhail Krylov <sqarert@gmail.com>]

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On Thu, Dec 01, 2022 at 02:00:58PM +0000, Robin Murphy wrote:
> On 2022-11-30 19:59, Mikhail Krylov wrote:
> > On Wed, Nov 30, 2022 at 11:07:32AM -0500, Alex Deucher wrote:
> > > On Wed, Nov 30, 2022 at 10:42 AM Robin Murphy <robin.murphy@arm.com> wrote:
> > > > 
> > > > On 2022-11-30 14:28, Alex Deucher wrote:
> > > > > On Wed, Nov 30, 2022 at 7:54 AM Robin Murphy <robin.murphy@arm.com> wrote:
> > > > > > 
> > > > > > On 2022-11-29 17:11, Mikhail Krylov wrote:
> > > > > > > On Tue, Nov 29, 2022 at 11:05:28AM -0500, Alex Deucher wrote:
> > > > > > > > On Tue, Nov 29, 2022 at 10:59 AM Mikhail Krylov <sqarert@gmail.com> wrote:
> > > > > > > > > 
> > > > > > > > > On Tue, Nov 29, 2022 at 09:44:19AM -0500, Alex Deucher wrote:
> > > > > > > > > > On Mon, Nov 28, 2022 at 3:48 PM Mikhail Krylov <sqarert@gmail.com> wrote:
> > > > > > > > > > > 
> > > > > > > > > > > On Mon, Nov 28, 2022 at 09:50:50AM -0500, Alex Deucher wrote:
> > > > > > > > > > > 
> > > > > > > > > > > > > > [excessive quoting removed]
> > > > > > > > > > > 
> > > > > > > > > > > > > So, is there any progress on this issue? I do understand it's not a high
> > > > > > > > > > > > > priority one, and today I've checked it on 6.0 kernel, and
> > > > > > > > > > > > > unfortunately, it still persists...
> > > > > > > > > > > > > 
> > > > > > > > > > > > > I'm considering writing a patch that will allow user to override
> > > > > > > > > > > > > need_dma32/dma_bits setting with a module parameter. I'll have some time
> > > > > > > > > > > > > after the New Year for that.
> > > > > > > > > > > > > 
> > > > > > > > > > > > > Is it at all possible that such a patch will be merged into kernel?
> > > > > > > > > > > > > 
> > > > > > > > > > > > On Mon, Nov 28, 2022 at 9:31 AM Mikhail Krylov <sqarert@gmail.com> wrote:
> > > > > > > > > > > > Unless someone familiar with HIMEM can figure out what is going wrong
> > > > > > > > > > > > we should just revert the patch.
> > > > > > > > > > > > 
> > > > > > > > > > > > Alex
> > > > > > > > > > > 
> > > > > > > > > > > 
> > > > > > > > > > > Okay, I was suggesting that mostly because
> > > > > > > > > > > 
> > > > > > > > > > > a) it works for me with dma_bits = 40 (I understand that's what it is
> > > > > > > > > > > without the original patch applied);
> > > > > > > > > > > 
> > > > > > > > > > > b) there's a hint of uncertainity on this line
> > > > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/radeon/radeon_device.c#n1359
> > > > > > > > > > > saying that for AGP dma_bits = 32 is the safest option, so apparently there are
> > > > > > > > > > > setups, unlike mine, where dma_bits = 32 is better than 40.
> > > > > > > > > > > 
> > > > > > > > > > > But I'm in no position to argue, just wanted to make myself clear.
> > > > > > > > > > > I'm okay with rebuilding the kernel for my machine until the original
> > > > > > > > > > > patch is reverted or any other fix is applied.
> > > > > > > > > > 
> > > > > > > > > > What GPU do you have and is it AGP?  If it is AGP, does setting
> > > > > > > > > > radeon.agpmode=-1 also fix it?
> > > > > > > > > > 
> > > > > > > > > > Alex
> > > > > > > > > 
> > > > > > > > > That is ATI Radeon X1950, and, unfortunately, radeon.agpmode=-1 doesn't
> > > > > > > > > help, it just makes 3D acceleration in games such as OpenArena stop
> > > > > > > > > working.
> > > > > > > > 
> > > > > > > > Just to confirm, is the board AGP or PCIe?
> > > > > > > > 
> > > > > > > > Alex
> > > > > > > 
> > > > > > > It is AGP. That's an old machine.
> > > > > > 
> > > > > > Can you check whether dma_addressing_limited() is actually returning the
> > > > > > expected result at the point of radeon_ttm_init()? Disabling highmem is
> > > > > > presumably just hiding whatever problem exists, by throwing away all
> > > > > >    >32-bit RAM such that use_dma32 doesn't matter.
> > > > > 
> > > > > The device in question only supports a 32 bit DMA mask so
> > > > > dma_addressing_limited() should return true.  Bounce buffers are not
> > > > > really usable on GPUs because they map so much memory.  If
> > > > > dma_addressing_limited() returns false, that would explain it.
> > > > 
> > > > Right, it appears to be the only part of the offending commit that
> > > > *could* reasonably make any difference, so I'm primarily wondering if
> > > > dma_get_required_mask() somehow gets confused.
> > > 
> > > Mikhail,
> > > 
> > > Can you see that dma_addressing_limited() and dma_get_required_mask()
> > > return in this case?
> > > 
> > > Alex
> > > 
> > > 
> > > > 
> > > > Thanks,
> > > > Robin.
> > 
> > Unfortunately, right now I don't have enough time for kernel
> > modifications and rebuilds (I will later!), so I did a quick-and-dirty
> > research with kprobe.
> > 
> > The problem is that dma_addressing_limited() seems to be inlined and
> > kprobe fails to intercept it.
> > 
> > But I managed to get the result of dma_get_required_mask(). It returns
> > 0x7fffffff (!) on the vanilla (with the patch, buggy) kernel:
> > $ sudo kprobe-perf 'r:dma_get_required_mask $retval'
> > Tracing kprobe dma_get_required_mask. Ctrl-C to end.
> >          modprobe-1244    [000] d...   105.582816: dma_get_required_mask: (radeon_ttm_init+0x61/0x240 [radeon] <- dma_get_required_mask) arg1=0x7fffffff
> > 
> > This function does not even get called in the kernel without the patch
> > that I built myself. I believe that's because ttm_bo_device_init()
> > doesn't call it without the patch.
> > 
> > Hope that helps at least a bit. If not, I'll be able to do more thorough
> > research in a couple of weeks, probably.
> 
> Hmm, just to clarify, what's your actual RAM layout? I've been assuming
> that the issue must be caused by unexpected DMA address truncation, but
> double-checking the older threads it seems that might not be the case.
> I just did a quick sanity-check of both HIGHMEM4G and HIGHMEM64G configs
> in a VM with either 2GB or 4GB of RAM assigned, and the
> dma_direct_get_required_mask() calculation seemed to return the
> appropriate result for all combinations.
> 
> Otherwise, the only significant difference of use_dma32 seems to be to
> switch TTM's allocation flags from GFP_HIGHUSER to GFP_DMA32. Could it
> just be that the highmem support somewhere between TTM and radeon has
> bitrotted, and it hasn't been noticed until this change because everyone
> still using a 32-bit system with highmem also happens not to be using a
> newer 40-bit-capable GPU? Or perhaps it never worked for AGP at all, in
> which case an explicit special case might be clearer?
> 
> diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
> index d33fec488713..acb2d534bff5 100644
> --- a/drivers/gpu/drm/radeon/radeon_ttm.c
> +++ b/drivers/gpu/drm/radeon/radeon_ttm.c
> @@ -696,6 +696,7 @@ int radeon_ttm_init(struct radeon_device *rdev)
>  			       rdev->ddev->anon_inode->i_mapping,
>  			       rdev->ddev->vma_offset_manager,
>  			       rdev->need_swiotlb,
> +			       rdev->flags & RADEON_IS_AGP ||
>  			       dma_addressing_limited(&rdev->pdev->dev));
>  	if (r) {
>  		DRM_ERROR("failed initializing buffer object driver(%d).\n", r);
> 
> Robin.

Sorry, not sure what you mean, I'll try to guess:

The bug exists on the stock 32-bit non-pae debian kernel (pae one also
works, but bug persists even there):

https://packages.debian.org/stable/kernel/linux-image-5.10.0-18-686

It has the following memory layout related options:

CONFIG_HIGHMEM4G=y
CONFIG_VMSPLIT_3G=y
CONFIG_HIGHMEM=y

The machine itself has 1.5G of RAM (1024M + 512M sticks).

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