[Xen-devel] [PATCH] Revert "swiotlb: remove SWIOTLB_MAP_ERROR"

[Arnd Bergmann <arnd@xxxxxxxx>]

This reverts commit b907e20508d0 ("swiotlb: remove SWIOTLB_MAP_ERROR"), which
introduced an overflow warning in configurations that have a larger
dma_addr_t than phys_addr_t:

In file included from include/linux/dma-direct.h:5,
                 from kernel/dma/swiotlb.c:23:
kernel/dma/swiotlb.c: In function 'swiotlb_tbl_map_single':
include/linux/dma-mapping.h:136:28: error: conversion from 'long long unsigned 
int' to 'phys_addr_t' {aka 'unsigned int'} changes value from 
'18446744073709551615' to '4294967295' [-Werror=overflow]
 #define DMA_MAPPING_ERROR  (~(dma_addr_t)0)
                            ^
kernel/dma/swiotlb.c:544:9: note: in expansion of macro 'DMA_MAPPING_ERROR'
  return DMA_MAPPING_ERROR;

The configuration that caused this is on 32-bit ARM, where the DMA address
space depends on the enabled hardware platforms, while the physical
address space depends on the type of MMU chosen (classic vs LPAE).

I tried a couple of alternative approaches, but the previous version
seems as good as any other, so I went back to that.

Fixes: b907e20508d0 ("swiotlb: remove SWIOTLB_MAP_ERROR")
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
 drivers/xen/swiotlb-xen.c | 4 ++--
 include/linux/swiotlb.h   | 3 +++
 kernel/dma/swiotlb.c      | 4 ++--
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 877baf2a94f4..57a98279bf4f 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -406,7 +406,7 @@ static dma_addr_t xen_swiotlb_map_page(struct device *dev, 
struct page *page,
 
        map = swiotlb_tbl_map_single(dev, start_dma_addr, phys, size, dir,
                                     attrs);
-       if (map == DMA_MAPPING_ERROR)
+       if (map == SWIOTLB_MAP_ERROR)
                return DMA_MAPPING_ERROR;
 
        dev_addr = xen_phys_to_bus(map);
@@ -557,7 +557,7 @@ xen_swiotlb_map_sg_attrs(struct device *hwdev, struct 
scatterlist *sgl,
                                                                 sg_phys(sg),
                                                                 sg->length,
                                                                 dir, attrs);
-                       if (map == DMA_MAPPING_ERROR) {
+                       if (map == SWIOTLB_MAP_ERROR) {
                                dev_warn(hwdev, "swiotlb buffer is full\n");
                                /* Don't panic here, we expect map_sg users
                                   to do proper error handling. */
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 361f62bb4a8e..a65a36551f58 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -44,6 +44,9 @@ enum dma_sync_target {
        SYNC_FOR_DEVICE = 1,
 };
 
+/* define the last possible byte of physical address space as a mapping error 
*/
+#define SWIOTLB_MAP_ERROR (~(phys_addr_t)0x0)
+
 extern phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
                                          dma_addr_t tbl_dma_addr,
                                          phys_addr_t phys, size_t size,
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 12059b78b631..922880b84387 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -541,7 +541,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
        spin_unlock_irqrestore(&io_tlb_lock, flags);
        if (!(attrs & DMA_ATTR_NO_WARN) && printk_ratelimit())
                dev_warn(hwdev, "swiotlb buffer is full (sz: %zd bytes)\n", 
size);
-       return DMA_MAPPING_ERROR;
+       return SWIOTLB_MAP_ERROR;
 found:
        io_tlb_used += nslots;
        spin_unlock_irqrestore(&io_tlb_lock, flags);
@@ -659,7 +659,7 @@ bool swiotlb_map(struct device *dev, phys_addr_t *phys, 
dma_addr_t *dma_addr,
        /* Oh well, have to allocate and map a bounce buffer. */
        *phys = swiotlb_tbl_map_single(dev, __phys_to_dma(dev, io_tlb_start),
                        *phys, size, dir, attrs);
-       if (*phys == DMA_MAPPING_ERROR)
+       if (*phys == SWIOTLB_MAP_ERROR)
                return false;
 
        /* Ensure that the address returned is DMA'ble */
-- 
2.20.0


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