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Subject[RFC PATCH V3 08/11] swiotlb: Add bounce buffer remap address setting function
Date
From: Tianyu Lan <Tianyu.Lan@microsoft.com>

For Hyper-V isolation VM with AMD SEV SNP, the bounce buffer(shared memory)
needs to be accessed via extra address space(e.g address above bit39).
Hyper-V code may remap extra address space outside of swiotlb. swiotlb_
bounce() needs to use remap virtual address to copy data from/to bounce
buffer. Add new interface swiotlb_set_bounce_remap() to do that.

Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
---
include/linux/swiotlb.h | 5 +++++
kernel/dma/swiotlb.c | 14 +++++++++++++-
2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 216854a5e513..43f53cf52f48 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -113,8 +113,13 @@ unsigned int swiotlb_max_segment(void);
size_t swiotlb_max_mapping_size(struct device *dev);
bool is_swiotlb_active(void);
void __init swiotlb_adjust_size(unsigned long size);
+void swiotlb_set_bounce_remap(unsigned char *vaddr);
#else
#define swiotlb_force SWIOTLB_NO_FORCE
+static inline void swiotlb_set_bounce_remap(unsigned char *vaddr)
+{
+}
+
static inline bool is_swiotlb_buffer(phys_addr_t paddr)
{
return false;
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 8ca7d505d61c..fbc827ab5fb4 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -70,6 +70,7 @@ struct io_tlb_mem *io_tlb_default_mem;
* not be bounced (unless SWIOTLB_FORCE is set).
*/
static unsigned int max_segment;
+static unsigned char *swiotlb_bounce_remap_addr;

static unsigned long default_nslabs = IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT;

@@ -334,6 +335,11 @@ void __init swiotlb_exit(void)
io_tlb_default_mem = NULL;
}

+void swiotlb_set_bounce_remap(unsigned char *vaddr)
+{
+ swiotlb_bounce_remap_addr = vaddr;
+}
+
/*
* Bounce: copy the swiotlb buffer from or back to the original dma location
*/
@@ -345,7 +351,13 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size
phys_addr_t orig_addr = mem->slots[index].orig_addr;
size_t alloc_size = mem->slots[index].alloc_size;
unsigned long pfn = PFN_DOWN(orig_addr);
- unsigned char *vaddr = phys_to_virt(tlb_addr);
+ unsigned char *vaddr;
+
+ if (swiotlb_bounce_remap_addr)
+ vaddr = swiotlb_bounce_remap_addr + tlb_addr -
+ io_tlb_default_mem->start;
+ else
+ vaddr = phys_to_virt(tlb_addr);

if (orig_addr == INVALID_PHYS_ADDR)
return;
--
2.25.1
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