[5.12 regression] ttm->pages NULL dereference with radeon driver

[Christian König]

Hi Takashi,

Am 07.05.21 um 17:08 schrieb Takashi Iwai:
> Hi,
>
> we've received a regression report showing NULL dereference Oops with
> radeon driver on 5.12 kernel:
>    https://bugzilla.opensuse.org/show_bug.cgi?id=1185516
>
> It turned out that the recent TTM cleanup / refactoring via commit
> 0575ff3d33cd ("drm/radeon: stop using pages with
> drm_prime_sg_to_page_addr_arrays v2") is the culprit.  On 5.12 kernel,
> ttm->pages is no longer allocated / set up, while the radeon driver
> still has a few places assuming the valid ttm->pages, and for the
> reporter (running the modesettig driver), radeon_gart_bind() hits the
> problem.
>
> A hackish patch below was confirmed to work, at least, but obviously
> we need a proper fix.
>
> Could you take a look at it?

If that's all then that looks trivial to me.

Going to provide a patch on Monday.

Thanks for the notice,
Christian.

>
>
> thanks,
>
> Takashi
>
> --- a/drivers/gpu/drm/radeon/radeon_gart.c
> +++ b/drivers/gpu/drm/radeon/radeon_gart.c
> @@ -253,7 +253,7 @@ void radeon_gart_unbind(struct radeon_de
>   	t = offset / RADEON_GPU_PAGE_SIZE;
>   	p = t / (PAGE_SIZE / RADEON_GPU_PAGE_SIZE);
>   	for (i = 0; i < pages; i++, p++) {
> -		if (rdev->gart.pages[p]) {
> +		if (1 /*rdev->gart.pages[p]*/) {
>   			rdev->gart.pages[p] = NULL;
>   			for (j = 0; j < (PAGE_SIZE / RADEON_GPU_PAGE_SIZE); j++, t++) {
>   				rdev->gart.pages_entry[t] = rdev->dummy_page.entry;
> @@ -301,7 +301,7 @@ int radeon_gart_bind(struct radeon_devic
>   	p = t / (PAGE_SIZE / RADEON_GPU_PAGE_SIZE);
>   
>   	for (i = 0; i < pages; i++, p++) {
> -		rdev->gart.pages[p] = pagelist[i];
> +		/* rdev->gart.pages[p] = pagelist[i]; */
>   		page_base = dma_addr[i];
>   		for (j = 0; j < (PAGE_SIZE / RADEON_GPU_PAGE_SIZE); j++, t++) {
>   			page_entry = radeon_gart_get_page_entry(page_base, flags);
> --- a/drivers/gpu/drm/radeon/radeon_ttm.c
> +++ b/drivers/gpu/drm/radeon/radeon_ttm.c
> @@ -360,6 +360,8 @@ static int radeon_ttm_tt_pin_userptr(str
>   
>   	if (current->mm != gtt->usermm)
>   		return -EPERM;
> +	if (!ttm->pages)
> +		return -EPERM;
>   
>   	if (gtt->userflags & RADEON_GEM_USERPTR_ANONONLY) {
>   		/* check that we only pin down anonymous memory
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