[RFC V2 PATCH 9/12] swiotlb: Add bounce buffer remap address setting function

[Tianyu Lan <ltykernel@gmail.com>]

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    | 13 ++++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index d9c9fc9ca5d2..3ccd08116683 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -82,8 +82,13 @@ 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 new_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 7c42df6e6100..5fd2db6aa149 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -94,6 +94,7 @@ static unsigned int io_tlb_index;
  * not be bounced (unless SWIOTLB_FORCE is set).
  */
 static unsigned int max_segment;
+static unsigned char *swiotlb_bounce_remap_addr;
 
 /*
  * We need to save away the original address corresponding to a mapped entry
@@ -421,6 +422,11 @@ void __init swiotlb_exit(void)
 	swiotlb_cleanup();
 }
 
+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
  */
@@ -428,7 +434,12 @@ static void swiotlb_bounce(phys_addr_t orig_addr, phys_addr_t tlb_addr,
 			   size_t size, enum dma_data_direction dir)
 {
 	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_start;
+	else
+		vaddr = phys_to_virt(tlb_addr);
 
 	if (PageHighMem(pfn_to_page(pfn))) {
 		/* The buffer does not have a mapping.  Map it in and copy */
-- 
2.25.1

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