[PATCH RFC] dma-direct: Try reallocation with GFP_DMA32 if possible

[PATCH RFC] dma-direct: Try reallocation with GFP_DMA32 if possible

[Takashi Iwai]

As the recent swiotlb bug revealed, we seem to have given up the
direct DMA allocation too early and felt back to swiotlb allocation.
The reason is that swiotlb allocator expected that dma_direct_alloc()
would try harder to get pages even below 64bit DMA mask with
GFP_DMA32, but the function doesn't do that but only deals with
GFP_DMA case.

This patch adds a similar fallback reallocation with GFP_DMA32 as
we've done with GFP_DMA.  The condition is that the coherent mask is
smaller than 64bit (i.e. some address limitation), and neither GFP_DMA
nor GFP_DMA32 is set beforehand.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

---

This is a resend of a test patch included in the previous thread
("swiotlb: Fix unexpected swiotlb_alloc_coherent() failures").

 lib/dma-direct.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/lib/dma-direct.c b/lib/dma-direct.c
index bbfb229aa067..970d39155618 100644
--- a/lib/dma-direct.c
+++ b/lib/dma-direct.c
@@ -84,6 +84,13 @@ void *dma_direct_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
 		__free_pages(page, page_order);
 		page = NULL;
 
+		if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
+		    dev->coherent_dma_mask < DMA_BIT_MASK(64) &&
+		    !(gfp & (GFP_DMA32 | GFP_DMA))) {
+			gfp |= GFP_DMA32;
+			goto again;
+		}
+
 		if (IS_ENABLED(CONFIG_ZONE_DMA) &&
 		    dev->coherent_dma_mask < DMA_BIT_MASK(32) &&
 		    !(gfp & GFP_DMA)) {
-- 
2.16.3

Re: [PATCH RFC] dma-direct: Try reallocation with GFP_DMA32 if possible

[Christoph Hellwig]

On Mon, Apr 16, 2018 at 05:18:19PM +0200, Takashi Iwai wrote:
> As the recent swiotlb bug revealed, we seem to have given up the
> direct DMA allocation too early and felt back to swiotlb allocation.
> The reason is that swiotlb allocator expected that dma_direct_alloc()
> would try harder to get pages even below 64bit DMA mask with
> GFP_DMA32, but the function doesn't do that but only deals with
> GFP_DMA case.
> 
> This patch adds a similar fallback reallocation with GFP_DMA32 as
> we've done with GFP_DMA.  The condition is that the coherent mask is
> smaller than 64bit (i.e. some address limitation), and neither GFP_DMA
> nor GFP_DMA32 is set beforehand.
> 
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> 
> ---
> 
> This is a resend of a test patch included in the previous thread
> ("swiotlb: Fix unexpected swiotlb_alloc_coherent() failures").

I like the patch, but as-is it doesn't apply.  Can you resend it against
latest Linus' tree?

Re: [PATCH RFC] dma-direct: Try reallocation with GFP_DMA32 if possible

[Christoph Hellwig]

On Mon, Apr 16, 2018 at 05:18:19PM +0200, Takashi Iwai wrote:
> As the recent swiotlb bug revealed, we seem to have given up the
> direct DMA allocation too early and felt back to swiotlb allocation.
> The reason is that swiotlb allocator expected that dma_direct_alloc()
> would try harder to get pages even below 64bit DMA mask with
> GFP_DMA32, but the function doesn't do that but only deals with
> GFP_DMA case.
> 
> This patch adds a similar fallback reallocation with GFP_DMA32 as
> we've done with GFP_DMA.  The condition is that the coherent mask is
> smaller than 64bit (i.e. some address limitation), and neither GFP_DMA
> nor GFP_DMA32 is set beforehand.
> 
> Signed-off-by: Takashi Iwai <tiwai-l3A5Bk7waGM@public.gmane.org>
> 
> ---
> 
> This is a resend of a test patch included in the previous thread
> ("swiotlb: Fix unexpected swiotlb_alloc_coherent() failures").

I like the patch, but as-is it doesn't apply.  Can you resend it against
latest Linus' tree?

Re: [PATCH RFC] dma-direct: Try reallocation with GFP_DMA32 if possible

[Takashi Iwai]

On Fri, 20 Apr 2018 11:47:02 +0200,
Christoph Hellwig wrote:
> 
> On Mon, Apr 16, 2018 at 05:18:19PM +0200, Takashi Iwai wrote:
> > As the recent swiotlb bug revealed, we seem to have given up the
> > direct DMA allocation too early and felt back to swiotlb allocation.
> > The reason is that swiotlb allocator expected that dma_direct_alloc()
> > would try harder to get pages even below 64bit DMA mask with
> > GFP_DMA32, but the function doesn't do that but only deals with
> > GFP_DMA case.
> > 
> > This patch adds a similar fallback reallocation with GFP_DMA32 as
> > we've done with GFP_DMA.  The condition is that the coherent mask is
> > smaller than 64bit (i.e. some address limitation), and neither GFP_DMA
> > nor GFP_DMA32 is set beforehand.
> > 
> > Signed-off-by: Takashi Iwai <tiwai@suse.de>
> > 
> > ---
> > 
> > This is a resend of a test patch included in the previous thread
> > ("swiotlb: Fix unexpected swiotlb_alloc_coherent() failures").
> 
> I like the patch, but as-is it doesn't apply.  Can you resend it against
> latest Linus' tree?

It's because it's written on the tree with another fix patch I sent
beforehand ("[PATCH 1/2] dma-direct: Don't repeat allocation for no-op
GFP_DMA").

Could you check that one at first?  I'm fine to rebase and resubmit
this one, if still preferred, though.


thanks,

Takashi

Re: [PATCH RFC] dma-direct: Try reallocation with GFP_DMA32 if possible

[Takashi Iwai]

On Fri, 20 Apr 2018 11:47:02 +0200,
Christoph Hellwig wrote:
> 
> On Mon, Apr 16, 2018 at 05:18:19PM +0200, Takashi Iwai wrote:
> > As the recent swiotlb bug revealed, we seem to have given up the
> > direct DMA allocation too early and felt back to swiotlb allocation.
> > The reason is that swiotlb allocator expected that dma_direct_alloc()
> > would try harder to get pages even below 64bit DMA mask with
> > GFP_DMA32, but the function doesn't do that but only deals with
> > GFP_DMA case.
> > 
> > This patch adds a similar fallback reallocation with GFP_DMA32 as
> > we've done with GFP_DMA.  The condition is that the coherent mask is
> > smaller than 64bit (i.e. some address limitation), and neither GFP_DMA
> > nor GFP_DMA32 is set beforehand.
> > 
> > Signed-off-by: Takashi Iwai <tiwai-l3A5Bk7waGM@public.gmane.org>
> > 
> > ---
> > 
> > This is a resend of a test patch included in the previous thread
> > ("swiotlb: Fix unexpected swiotlb_alloc_coherent() failures").
> 
> I like the patch, but as-is it doesn't apply.  Can you resend it against
> latest Linus' tree?

It's because it's written on the tree with another fix patch I sent
beforehand ("[PATCH 1/2] dma-direct: Don't repeat allocation for no-op
GFP_DMA").

Could you check that one at first?  I'm fine to rebase and resubmit
this one, if still preferred, though.


thanks,

Takashi

Re: [PATCH RFC] dma-direct: Try reallocation with GFP_DMA32 if possible

[Christoph Hellwig]

On Fri, Apr 20, 2018 at 11:58:58AM +0200, Takashi Iwai wrote:
> It's because it's written on the tree with another fix patch I sent
> beforehand ("[PATCH 1/2] dma-direct: Don't repeat allocation for no-op
> GFP_DMA").
> 
> Could you check that one at first?  I'm fine to rebase and resubmit
> this one, if still preferred, though.

That one looks fine, too.  I'll add it to my patch queue.

Re: [PATCH RFC] dma-direct: Try reallocation with GFP_DMA32 if possible

[Christoph Hellwig]

On Fri, Apr 20, 2018 at 11:58:58AM +0200, Takashi Iwai wrote:
> It's because it's written on the tree with another fix patch I sent
> beforehand ("[PATCH 1/2] dma-direct: Don't repeat allocation for no-op
> GFP_DMA").
> 
> Could you check that one at first?  I'm fine to rebase and resubmit
> this one, if still preferred, though.

That one looks fine, too.  I'll add it to my patch queue.