Re: [PATCH 09/10] xen/arm: introduce phys/dma translations in xen_dma_sync_for_*
On Thu, 21 May 2020 at 21:08, Stefano Stabellini wrote:
>
> On Thu, 21 May 2020, Julien Grall wrote:
> > > @@ -97,8 +98,7 @@ bool xen_arch_need_swiotlb(struct device *dev,
> > >phys_addr_t phys,
> > >dma_addr_t dev_addr)
> > > {
> > > - unsigned int xen_pfn = XEN_PFN_DOWN(phys);
> > > - unsigned int bfn = XEN_PFN_DOWN(dev_addr);
> > > + unsigned int bfn = XEN_PFN_DOWN(dma_to_phys(dev, dev_addr));
> > > /*
> > > * The swiotlb buffer should be used if
> > > @@ -115,7 +115,7 @@ bool xen_arch_need_swiotlb(struct device *dev,
> > > * require a bounce buffer because the device doesn't support coherent
> > > * memory and we are not able to flush the cache.
> > > */
> > > - return (!hypercall_cflush && (xen_pfn != bfn) &&
> > > + return (!hypercall_cflush && !pfn_valid(bfn) &&
> >
> > I believe this change is incorrect. The bfn is a frame based on Xen page
> > granularity (always 4K) while pfn_valid() is expecting a frame based on the
> > Kernel page granularity.
>
> Given that kernel granularity >= xen granularity it looks like it would
> be safe to use PFN_DOWN instead of XEN_PFN_DOWN:
>
> unsigned int bfn = PFN_DOWN(dma_to_phys(dev, dev_addr));
Yes. But is the change worth it though? pfn_valid() is definitely
going to be more expensive than the current check.
Cheers,
Re: [PATCH 09/10] xen/arm: introduce phys/dma translations in xen_dma_sync_for_*
On Thu, 21 May 2020, Julien Grall wrote:
> > @@ -97,8 +98,7 @@ bool xen_arch_need_swiotlb(struct device *dev,
> >phys_addr_t phys,
> >dma_addr_t dev_addr)
> > {
> > - unsigned int xen_pfn = XEN_PFN_DOWN(phys);
> > - unsigned int bfn = XEN_PFN_DOWN(dev_addr);
> > + unsigned int bfn = XEN_PFN_DOWN(dma_to_phys(dev, dev_addr));
> > /*
> > * The swiotlb buffer should be used if
> > @@ -115,7 +115,7 @@ bool xen_arch_need_swiotlb(struct device *dev,
> > * require a bounce buffer because the device doesn't support coherent
> > * memory and we are not able to flush the cache.
> > */
> > - return (!hypercall_cflush && (xen_pfn != bfn) &&
> > + return (!hypercall_cflush && !pfn_valid(bfn) &&
>
> I believe this change is incorrect. The bfn is a frame based on Xen page
> granularity (always 4K) while pfn_valid() is expecting a frame based on the
> Kernel page granularity.
Given that kernel granularity >= xen granularity it looks like it would
be safe to use PFN_DOWN instead of XEN_PFN_DOWN:
unsigned int bfn = PFN_DOWN(dma_to_phys(dev, dev_addr));
return (!hypercall_cflush && !pfn_valid(bfn) &&
Re: [PATCH 09/10] xen/arm: introduce phys/dma translations in xen_dma_sync_for_*
Hi,
On 21/05/2020 00:45, Stefano Stabellini wrote:
From: Stefano Stabellini
Add phys_to_dma/dma_to_phys calls to
xen_dma_sync_for_cpu, xen_dma_sync_for_device, and
xen_arch_need_swiotlb.
In xen_arch_need_swiotlb, take the opportunity to switch to the simpler
pfn_valid check we use everywhere else.
dma_cache_maint is fixed by the next patch.
Like patch #8, this explains what the code is doing not why this is
necessary.
Signed-off-by: Stefano Stabellini
---
arch/arm/xen/mm.c | 10 +-
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index f2414ea40a79..7639251bcc79 100644
--- a/arch/arm/xen/mm.c
+++ b/arch/arm/xen/mm.c
@@ -1,5 +1,6 @@
// SPDX-License-Identifier: GPL-2.0-only
#include
+#include
#include
#include
#include
@@ -75,7 +76,7 @@ void xen_dma_sync_for_cpu(struct device *dev, dma_addr_t
handle,
phys_addr_t paddr, size_t size,
enum dma_data_direction dir)
{
- if (pfn_valid(PFN_DOWN(handle)))
+ if (pfn_valid(PFN_DOWN(dma_to_phys(dev, handle
arch_sync_dma_for_cpu(paddr, size, dir);
else if (dir != DMA_TO_DEVICE)
dma_cache_maint(handle, size, GNTTAB_CACHE_INVAL);
@@ -85,7 +86,7 @@ void xen_dma_sync_for_device(struct device *dev, dma_addr_t
handle,
phys_addr_t paddr, size_t size,
enum dma_data_direction dir)
{
- if (pfn_valid(PFN_DOWN(handle)))
+ if (pfn_valid(PFN_DOWN(dma_to_phys(dev, handle
arch_sync_dma_for_device(paddr, size, dir);
else if (dir == DMA_FROM_DEVICE)
dma_cache_maint(handle, size, GNTTAB_CACHE_INVAL);
@@ -97,8 +98,7 @@ bool xen_arch_need_swiotlb(struct device *dev,
phys_addr_t phys,
dma_addr_t dev_addr)
{
- unsigned int xen_pfn = XEN_PFN_DOWN(phys);
- unsigned int bfn = XEN_PFN_DOWN(dev_addr);
+ unsigned int bfn = XEN_PFN_DOWN(dma_to_phys(dev, dev_addr));
/*
* The swiotlb buffer should be used if
@@ -115,7 +115,7 @@ bool xen_arch_need_swiotlb(struct device *dev,
* require a bounce buffer because the device doesn't support coherent
* memory and we are not able to flush the cache.
*/
- return (!hypercall_cflush && (xen_pfn != bfn) &&
+ return (!hypercall_cflush && !pfn_valid(bfn) &&
I believe this change is incorrect. The bfn is a frame based on Xen page
granularity (always 4K) while pfn_valid() is expecting a frame based on
the Kernel page granularity.
!dev_is_dma_coherent(dev));
}
Cheers,
--
Julien Grall
