Subject: [PATCH V5 09/12] x86/Swiotlb: Add Swiotlb bounce buffer remap function for HV IVM

From: Tianyu Lan <[email-masked]>
Date: Tue, 14 Sep 2021 09:39:10 -0400

From: Tianyu Lan <[email-masked]>

In Isolation VM with AMD SEV, bounce buffer needs to be accessed via
extra address space which is above shared_gpa_boundary
(E.G 39 bit address line) reported by Hyper-V CPUID ISOLATION_CONFIG.
The access physical address will be original physical address +
shared_gpa_boundary. The shared_gpa_boundary in the AMD SEV SNP
spec is called virtual top of memory(vTOM). Memory addresses below
vTOM are automatically treated as private while memory above
vTOM is treated as shared.

Expose swiotlb_unencrypted_base for platforms to set unencrypted
memory base offset and call memremap() to map bounce buffer in the
swiotlb code, store map address and use the address to copy data
from/to swiotlb bounce buffer.

Signed-off-by: Tianyu Lan <[email-masked]>
---
Change since v4:
	* Expose swiotlb_unencrypted_base to set unencrypted memory
	  offset.
	* Use memremap() to map bounce buffer if swiotlb_unencrypted_
	  base is set.

Change since v1:
	* Make swiotlb_init_io_tlb_mem() return error code and return
          error when dma_map_decrypted() fails.
---
 include/linux/swiotlb.h |  6 ++++++
 kernel/dma/swiotlb.c    | 41 +++++++++++++++++++++++++++++++++++------
 2 files changed, 41 insertions(+), 6 deletions(-)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index b0cb2a9973f4..4998ed44ae3d 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -72,6 +72,9 @@ extern enum swiotlb_force swiotlb_force;
  * @end:	The end address of the swiotlb memory pool. Used to do a quick
  *		range check to see if the memory was in fact allocated by this
  *		API.
+ * @vaddr:	The vaddr of the swiotlb memory pool. The swiotlb
+ *		memory pool may be remapped in the memory encrypted case and store
+ *		virtual address for bounce buffer operation.
  * @nslabs:	The number of IO TLB blocks (in groups of 64) between @start and
  *		@end. For default swiotlb, this is command line adjustable via
  *		setup_io_tlb_npages.
@@ -91,6 +94,7 @@ extern enum swiotlb_force swiotlb_force;
 struct io_tlb_mem {
 	phys_addr_t start;
 	phys_addr_t end;
+	void *vaddr;
 	unsigned long nslabs;
 	unsigned long used;
 	unsigned int index;
@@ -185,4 +189,6 @@ static inline bool is_swiotlb_for_alloc(struct device *dev)
 }
 #endif /* CONFIG_DMA_RESTRICTED_POOL */
 
+extern phys_addr_t swiotlb_unencrypted_base;
+
 #endif /* __LINUX_SWIOTLB_H */
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 87c40517e822..9e30cc4bd872 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -50,6 +50,7 @@
 #include <asm/io.h>
 #include <asm/dma.h>
 
+#include <linux/io.h>
 #include <linux/init.h>
 #include <linux/memblock.h>
 #include <linux/iommu-helper.h>
@@ -72,6 +73,8 @@ enum swiotlb_force swiotlb_force;
 
 struct io_tlb_mem io_tlb_default_mem;
 
+phys_addr_t swiotlb_unencrypted_base;
+
 /*
  * Max segment that we can provide which (if pages are contingous) will
  * not be bounced (unless SWIOTLB_FORCE is set).
@@ -175,7 +178,7 @@ void __init swiotlb_update_mem_attributes(void)
 	memset(vaddr, 0, bytes);
 }
 
-static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
+static int swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
 				    unsigned long nslabs, bool late_alloc)
 {
 	void *vaddr = phys_to_virt(start);
@@ -196,13 +199,34 @@ static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
 		mem->slots[i].orig_addr = INVALID_PHYS_ADDR;
 		mem->slots[i].alloc_size = 0;
 	}
+
+	if (set_memory_decrypted((unsigned long)vaddr, bytes >> PAGE_SHIFT))
+		return -EFAULT;
+
+	/*
+	 * Map memory in the unencrypted physical address space when requested
+	 * (e.g. for Hyper-V AMD SEV-SNP Isolation VMs).
+	 */
+	if (swiotlb_unencrypted_base) {
+		phys_addr_t paddr = __pa(vaddr) + swiotlb_unencrypted_base;
+
+		vaddr = memremap(paddr, bytes, MEMREMAP_WB);
+		if (!vaddr) {
+			pr_err("Failed to map the unencrypted memory.\n");
+			return -ENOMEM;
+		}
+	}
+
 	memset(vaddr, 0, bytes);
+	mem->vaddr = vaddr;
+	return 0;
 }
 
 int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 {
 	struct io_tlb_mem *mem = &io_tlb_default_mem;
 	size_t alloc_size;
+	int ret;
 
 	if (swiotlb_force == SWIOTLB_NO_FORCE)
 		return 0;
@@ -217,7 +241,11 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
 		panic("%s: Failed to allocate %zu bytes align=0x%lx\n",
 		      __func__, alloc_size, PAGE_SIZE);
 
-	swiotlb_init_io_tlb_mem(mem, __pa(tlb), nslabs, false);
+	ret = swiotlb_init_io_tlb_mem(mem, __pa(tlb), nslabs, false);
+	if (ret) {
+		memblock_free(__pa(mem), alloc_size);
+		return ret;
+	}
 
 	if (verbose)
 		swiotlb_print_info();
@@ -304,7 +332,7 @@ int
 swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 {
 	struct io_tlb_mem *mem = &io_tlb_default_mem;
-	unsigned long bytes = nslabs << IO_TLB_SHIFT;
+	int ret;
 
 	if (swiotlb_force == SWIOTLB_NO_FORCE)
 		return 0;
@@ -318,8 +346,9 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
 	if (!mem->slots)
 		return -ENOMEM;
 
-	set_memory_decrypted((unsigned long)tlb, bytes >> PAGE_SHIFT);
-	swiotlb_init_io_tlb_mem(mem, virt_to_phys(tlb), nslabs, true);
+	ret = swiotlb_init_io_tlb_mem(mem, virt_to_phys(tlb), nslabs, true);
+	if (ret)
+		return ret;
 
 	swiotlb_print_info();
 	swiotlb_set_max_segment(mem->nslabs << IO_TLB_SHIFT);
@@ -371,7 +400,7 @@ 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 = mem->vaddr + tlb_addr - mem->start;
 	unsigned int tlb_offset, orig_addr_offset;
 
 	if (orig_addr == INVALID_PHYS_ADDR)
-- 
2.25.1