system/memory: Make ram device region directly accessible
This basically reverts 4a2e242bbb30 ("memory: Don't use memcpy for ram_device regions") to make ram device region directly accessible again. With this, the bounce buffer is bypassed in address_space_map() when a ram device region is involved, potentially avoid to overrun the (small) bounce buffer. Reported-by: Julia Graham <jugraham@redhat.com> Suggested-by: Michael S. Tsirkin <mst@redhat.com> Suggested-by: Peter Xu <peterx@redhat.com> Suggested-by: Richard Henderson <richard.henderson@linaro.org> Suggested-by: Peter Maydell <peter.maydell@linaro.org> Signed-off-by: Gavin Shan <gshan@redhat.com> Reviewed-by: Peter Maydell <peter.maydell@linaro.org> Link: https://lore.kernel.org/r/20260728031731.286666-4-gshan@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com>
Gavin Shan committed
Jul 28, 2026 at 13:17 UTC
ff77a515113f052cc5fc571b6a328142fdfcf220
3 files changed
+3
-51
include/system/memory.h
+2
-9
@@ -2718,15 +2718,8 @@ static inline bool memory_region_supports_direct_access(const MemoryRegion *mr)
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if (memory_region_is_romd(mr)) {
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return true;
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}
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- if (!memory_region_is_ram(mr)) {
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- return false;
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- }
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- /*
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- * RAM DEVICE regions can be accessed directly using memcpy, but it might
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- * be MMIO and access using mempy can be wrong (e.g., using instructions not
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- * intended for MMIO access). So we treat this as IO.
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- */
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- return !memory_region_is_ram_device(mr);
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+
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+ return memory_region_is_ram(mr);
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}
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static inline bool memory_access_is_direct(const MemoryRegion *mr,
system/memory.c
+1
-40
@@ -1364,43 +1364,6 @@ const MemoryRegionOps unassigned_mem_ops = {
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.endianness = DEVICE_NATIVE_ENDIAN,
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};
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-static uint64_t memory_region_ram_device_read(void *opaque,
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- hwaddr addr, unsigned size)
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-{
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- MemoryRegion *mr = opaque;
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- uint64_t data = ldn_he_p(mr->ram_block->host + addr, size);
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-
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- trace_memory_region_ram_device_read(get_cpu_index(), mr, addr, data, size);
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-
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- return data;
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-}
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-
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-static void memory_region_ram_device_write(void *opaque, hwaddr addr,
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- uint64_t data, unsigned size)
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-{
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- MemoryRegion *mr = opaque;
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-
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- trace_memory_region_ram_device_write(get_cpu_index(), mr, addr, data, size);
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-
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- stn_he_p(mr->ram_block->host + addr, size, data);
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-}
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-
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-static const MemoryRegionOps ram_device_mem_ops = {
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- .read = memory_region_ram_device_read,
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- .write = memory_region_ram_device_write,
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- .endianness = HOST_BIG_ENDIAN ? DEVICE_BIG_ENDIAN : DEVICE_LITTLE_ENDIAN,
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- .valid = {
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- .min_access_size = 1,
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- .max_access_size = 8,
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- .unaligned = true,
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- },
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- .impl = {
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- .min_access_size = 1,
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- .max_access_size = 8,
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- .unaligned = true,
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- },
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-};
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-
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bool memory_region_access_valid(MemoryRegion *mr,
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hwaddr addr,
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unsigned size,
@@ -1692,10 +1655,8 @@ void memory_region_init_ram_device_ptr(MemoryRegion *mr, Object *owner,
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const char *name, uint64_t size,
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void *ptr)
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{
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- memory_region_init_io(mr, owner, &ram_device_mem_ops, mr, name, size);
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- mr->ram = true;
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+ memory_region_init_ram_ptr(mr, owner, name, size, ptr);
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mr->ram_device = true;
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- memory_region_set_ram_ptr(mr, size, ptr);
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}
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void memory_region_init_alias(MemoryRegion *mr, Object *owner,
system/trace-events
-2
@@ -20,8 +20,6 @@ memory_region_ops_read(int cpu_index, void *mr, uint64_t addr, uint64_t value, u
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memory_region_ops_write(int cpu_index, void *mr, uint64_t addr, uint64_t value, unsigned size, const char *name) "cpu %d mr %p addr 0x%"PRIx64" value 0x%"PRIx64" size %u name '%s'"
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memory_region_subpage_read(int cpu_index, void *mr, uint64_t offset, uint64_t value, unsigned size) "cpu %d mr %p offset 0x%"PRIx64" value 0x%"PRIx64" size %u"
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memory_region_subpage_write(int cpu_index, void *mr, uint64_t offset, uint64_t value, unsigned size) "cpu %d mr %p offset 0x%"PRIx64" value 0x%"PRIx64" size %u"
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-memory_region_ram_device_read(int cpu_index, void *mr, uint64_t addr, uint64_t value, unsigned size) "cpu %d mr %p addr 0x%"PRIx64" value 0x%"PRIx64" size %u"
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-memory_region_ram_device_write(int cpu_index, void *mr, uint64_t addr, uint64_t value, unsigned size) "cpu %d mr %p addr 0x%"PRIx64" value 0x%"PRIx64" size %u"
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memory_region_sync_dirty(const char *mr, const char *listener, int global) "mr '%s' listener '%s' synced (global=%d)"
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flatview_new(void *view, void *root) "%p (root %p)"
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flatview_destroy(void *view, void *root) "%p (root %p)"