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Re: [PATCH 09/10] xen/arm: introduce phys/dma translations in xen_dma_sync_for_*


On 21/05/2020 00:45, Stefano Stabellini wrote:
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>

Add phys_to_dma/dma_to_phys calls to
xen_dma_sync_for_cpu, xen_dma_sync_for_device, and

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 <stefano.stabellini@xxxxxxxxxx>
  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 <linux/cpu.h>
+#include <linux/dma-direct.h>
  #include <linux/dma-noncoherent.h>
  #include <linux/gfp.h>
  #include <linux/highmem.h>
@@ -75,7 +76,7 @@ void xen_dma_sync_for_cpu(struct device *dev, dma_addr_t 
                          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 
                             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.



Julien Grall



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