On Wed, Nov 12, 2014 at 01:39:05PM +0100, Thierry Reding wrote:
From: Thierry Reding treding@nvidia.com
dma_alloc_coherent() returns a kernel virtual address that is part of the linear range. Passing such an address to virt_to_page() is illegal on non-coherent architectures. This causes the kernel to oops on 64-bit ARM because the struct page * obtained from virt_to_page() points to unmapped memory.
Oh! That is not good!
This commit fixes this by using phys_to_page() since we get a physical address from dma_alloc_coherent(). Note that this is not a proper fix because if an IOMMU is set up to translate addresses for the GPU this address will be an I/O virtual address rather than a physical one. The proper fix probably involves not getting a pointer to the struct page in the first place, but that would be a much more intrusive change, if at all possible.
What type of caching types are there on ARM? We use the 'struct page' on the set_pages_to_[wc|uc|wb] but all of those are X86 specfic.
But I think you could by passing the 'struct dma_page' instead of 'struct page' (and the array uses) around. That should solve the touching of 'struct page' and we can treat it as an opaque type.
Until that time, this temporary fix will allow TTM to work on 32-bit and 64-bit ARM as well, provided that no IOMMU translations are enabled for the GPU.
Is there a way to query the 'struct device' to see if the IOMMU translation is enabled/disabled for said device?
Now your patch looks to get the 'struct page' by doing some form of translation. Could you explain to me which type of memory have a 'struct page' and which ones do not ?
It is OK if you explain this in nauseating details :-)
Signed-off-by: Thierry Reding treding@nvidia.com
Arnd, I realize that this isn't a proper fix according to what we discussed on IRC yesterday, but I can't see a way to remove access to the pages array that would be as simple as this. I've marked this as RFC in the hope that it will trigger some discussion that will lead to a proper solution.
drivers/gpu/drm/ttm/ttm_page_alloc_dma.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c index c96db433f8af..d7993985752c 100644 --- a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c +++ b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c @@ -343,7 +343,11 @@ static struct dma_page *__ttm_dma_alloc_page(struct dma_pool *pool) &d_page->dma, pool->gfp_flags); if (d_page->vaddr) +#if defined(CONFIG_ARM) || defined(CONFIG_ARM64)
d_page->p = phys_to_page(d_page->dma);+#else d_page->p = virt_to_page(d_page->vaddr); +#endif else { kfree(d_page); d_page = NULL; -- 2.1.3