[RFC PATCH v2 14/20] x86: DMA support for memory encryption

From: Tom Lendacky
Date: Mon Aug 22 2016 - 18:54:59 EST

Since DMA addresses will effectively look like 48-bit addresses when the
memory encryption mask is set, SWIOTLB is needed if the DMA mask of the
device performing the DMA does not support 48-bits. SWIOTLB will be
initialized to create un-encrypted bounce buffers for use by these devices.

Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
arch/x86/include/asm/dma-mapping.h | 5 ++-
arch/x86/include/asm/mem_encrypt.h | 6 +++
arch/x86/kernel/pci-dma.c | 11 ++++--
arch/x86/kernel/pci-nommu.c | 2 +
arch/x86/kernel/pci-swiotlb.c | 8 +++--
arch/x86/mm/mem_encrypt.c | 22 ++++++++++++
include/linux/swiotlb.h | 1 +
init/main.c | 13 +++++++
lib/swiotlb.c | 64 ++++++++++++++++++++++++++++++++----
9 files changed, 115 insertions(+), 17 deletions(-)

diff --git a/arch/x86/include/asm/dma-mapping.h b/arch/x86/include/asm/dma-mapping.h
index 4446162..c9cdcae 100644
--- a/arch/x86/include/asm/dma-mapping.h
+++ b/arch/x86/include/asm/dma-mapping.h
@@ -12,6 +12,7 @@
#include <asm/io.h>
#include <asm/swiotlb.h>
#include <linux/dma-contiguous.h>
+#include <asm/mem_encrypt.h>

#ifdef CONFIG_ISA
# define ISA_DMA_BIT_MASK DMA_BIT_MASK(24)
@@ -69,12 +70,12 @@ static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size)

static inline dma_addr_t phys_to_dma(struct device *dev, phys_addr_t paddr)
{
- return paddr;
+ return paddr | sme_me_mask;
}

static inline phys_addr_t dma_to_phys(struct device *dev, dma_addr_t daddr)
{
- return daddr;
+ return daddr & ~sme_me_mask;
}
#endif /* CONFIG_X86_DMA_REMAP */

diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index 5616ed1..384fdfb 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -33,6 +33,12 @@ void __init sme_early_mem_dec(resource_size_t paddr,

void __init sme_early_init(void);

+/* Architecture __weak replacement functions */
+void __init mem_encrypt_init(void);
+
+unsigned long swiotlb_get_me_mask(void);
+void swiotlb_set_mem_dec(void *vaddr, unsigned long size);
+
#define __sme_pa(x) (__pa((x)) | sme_me_mask)
#define __sme_pa_nodebug(x) (__pa_nodebug((x)) | sme_me_mask)

diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index d30c377..0ce28df 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -92,9 +92,12 @@ again:
/* CMA can be used only in the context which permits sleeping */
if (gfpflags_allow_blocking(flag)) {
page = dma_alloc_from_contiguous(dev, count, get_order(size));
- if (page && page_to_phys(page) + size > dma_mask) {
- dma_release_from_contiguous(dev, page, count);
- page = NULL;
+ if (page) {
+ addr = phys_to_dma(dev, page_to_phys(page));
+ if (addr + size > dma_mask) {
+ dma_release_from_contiguous(dev, page, count);
+ page = NULL;
+ }
}
}
/* fallback */
@@ -103,7 +106,7 @@ again:
if (!page)
return NULL;

- addr = page_to_phys(page);
+ addr = phys_to_dma(dev, page_to_phys(page));
if (addr + size > dma_mask) {
__free_pages(page, get_order(size));

diff --git a/arch/x86/kernel/pci-nommu.c b/arch/x86/kernel/pci-nommu.c
index 00e71ce..922c10d 100644
--- a/arch/x86/kernel/pci-nommu.c
+++ b/arch/x86/kernel/pci-nommu.c
@@ -30,7 +30,7 @@ static dma_addr_t nommu_map_page(struct device *dev, struct page *page,
enum dma_data_direction dir,
unsigned long attrs)
{
- dma_addr_t bus = page_to_phys(page) + offset;
+ dma_addr_t bus = phys_to_dma(dev, page_to_phys(page)) + offset;
WARN_ON(size == 0);
if (!check_addr("map_single", dev, bus, size))
return DMA_ERROR_CODE;
diff --git a/arch/x86/kernel/pci-swiotlb.c b/arch/x86/kernel/pci-swiotlb.c
index b47edb8..34a9e524 100644
--- a/arch/x86/kernel/pci-swiotlb.c
+++ b/arch/x86/kernel/pci-swiotlb.c
@@ -12,6 +12,8 @@
#include <asm/dma.h>
#include <asm/xen/swiotlb-xen.h>
#include <asm/iommu_table.h>
+#include <asm/mem_encrypt.h>
+
int swiotlb __read_mostly;

void *x86_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
@@ -64,13 +66,15 @@ static struct dma_map_ops swiotlb_dma_ops = {
* pci_swiotlb_detect_override - set swiotlb to 1 if necessary
*
* This returns non-zero if we are forced to use swiotlb (by the boot
- * option).
+ * option). If memory encryption is enabled then swiotlb will be set
+ * to 1 so that bounce buffers are allocated and used for devices that
+ * do not support the addressing range required for the encryption mask.
*/
int __init pci_swiotlb_detect_override(void)
{
int use_swiotlb = swiotlb | swiotlb_force;

- if (swiotlb_force)
+ if (swiotlb_force || sme_me_mask)
swiotlb = 1;

return use_swiotlb;
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index b0f39c5..6b2e8bf 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -12,6 +12,8 @@

#include <linux/init.h>
#include <linux/mm.h>
+#include <linux/dma-mapping.h>
+#include <linux/swiotlb.h>

#include <asm/mem_encrypt.h>
#include <asm/cacheflush.h>
@@ -172,3 +174,23 @@ void __init sme_early_init(void)
for (i = 0; i < ARRAY_SIZE(protection_map); i++)
protection_map[i] = __pgprot(pgprot_val(protection_map[i]) | sme_me_mask);
}
+
+/* Architecture __weak replacement functions */
+void __init mem_encrypt_init(void)
+{
+ if (!sme_me_mask)
+ return;
+
+ /* Make SWIOTLB use an unencrypted DMA area */
+ swiotlb_clear_encryption();
+}
+
+unsigned long swiotlb_get_me_mask(void)
+{
+ return sme_me_mask;
+}
+
+void swiotlb_set_mem_dec(void *vaddr, unsigned long size)
+{
+ sme_set_mem_dec(vaddr, size);
+}
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 5f81f8a..5c909fc 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -29,6 +29,7 @@ int swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose);
extern unsigned long swiotlb_nr_tbl(void);
unsigned long swiotlb_size_or_default(void);
extern int swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs);
+extern void __init swiotlb_clear_encryption(void);

/*
* Enumeration for sync targets
diff --git a/init/main.c b/init/main.c
index a8a58e2..82c7cd9 100644
--- a/init/main.c
+++ b/init/main.c
@@ -458,6 +458,10 @@ void __init __weak thread_stack_cache_init(void)
}
#endif

+void __init __weak mem_encrypt_init(void)
+{
+}
+
/*
* Set up kernel memory allocators
*/
@@ -598,6 +602,15 @@ asmlinkage __visible void __init start_kernel(void)
*/
locking_selftest();

+ /*
+ * This needs to be called before any devices perform DMA
+ * operations that might use the swiotlb bounce buffers.
+ * This call will mark the bounce buffers as un-encrypted so
+ * that the usage of them will not cause "plain-text" data
+ * to be decrypted when accessed.
+ */
+ mem_encrypt_init();
+
#ifdef CONFIG_BLK_DEV_INITRD
if (initrd_start && !initrd_below_start_ok &&
page_to_pfn(virt_to_page((void *)initrd_start)) < min_low_pfn) {
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 22e13a0..15d5741 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -131,6 +131,26 @@ unsigned long swiotlb_size_or_default(void)
return size ? size : (IO_TLB_DEFAULT_SIZE);
}

+/*
+ * Support for memory encryption. If memory encryption is supported, then an
+ * override to these functions will be provided.
+ */
+unsigned long __weak swiotlb_get_me_mask(void)
+{
+ return 0;
+}
+
+void __weak swiotlb_set_mem_dec(void *vaddr, unsigned long size)
+{
+}
+
+/* For swiotlb, clear memory encryption mask from dma addresses */
+static dma_addr_t swiotlb_phys_to_dma(struct device *hwdev,
+ phys_addr_t address)
+{
+ return phys_to_dma(hwdev, address) & ~swiotlb_get_me_mask();
+}
+
/* Note that this doesn't work with highmem page */
static dma_addr_t swiotlb_virt_to_bus(struct device *hwdev,
volatile void *address)
@@ -159,6 +179,30 @@ void swiotlb_print_info(void)
bytes >> 20, vstart, vend - 1);
}

+/*
+ * If memory encryption is active, the DMA address for an encrypted page may
+ * be beyond the range of the device. If bounce buffers are required be sure
+ * that they are not on an encrypted page. This should be called before the
+ * iotlb area is used.
+ */
+void __init swiotlb_clear_encryption(void)
+{
+ void *vaddr;
+ unsigned long bytes;
+
+ if (no_iotlb_memory || !io_tlb_start || late_alloc)
+ return;
+
+ vaddr = phys_to_virt(io_tlb_start);
+ bytes = PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT);
+ swiotlb_set_mem_dec(vaddr, bytes);
+ memset(vaddr, 0, bytes);
+
+ vaddr = phys_to_virt(io_tlb_overflow_buffer);
+ bytes = PAGE_ALIGN(io_tlb_overflow);
+ swiotlb_set_mem_dec(vaddr, bytes);
+}
+
int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
{
void *v_overflow_buffer;
@@ -294,6 +338,8 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
io_tlb_start = virt_to_phys(tlb);
io_tlb_end = io_tlb_start + bytes;

+ /* Keep TLB in unencrypted memory if memory encryption is active */
+ swiotlb_set_mem_dec(tlb, bytes);
memset(tlb, 0, bytes);

/*
@@ -304,6 +350,8 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
if (!v_overflow_buffer)
goto cleanup2;

+ /* Keep overflow in unencrypted memory if memory encryption is active */
+ swiotlb_set_mem_dec(v_overflow_buffer, io_tlb_overflow);
io_tlb_overflow_buffer = virt_to_phys(v_overflow_buffer);

/*
@@ -541,7 +589,7 @@ static phys_addr_t
map_single(struct device *hwdev, phys_addr_t phys, size_t size,
enum dma_data_direction dir)
{
- dma_addr_t start_dma_addr = phys_to_dma(hwdev, io_tlb_start);
+ dma_addr_t start_dma_addr = swiotlb_phys_to_dma(hwdev, io_tlb_start);

return swiotlb_tbl_map_single(hwdev, start_dma_addr, phys, size, dir);
}
@@ -659,7 +707,7 @@ swiotlb_alloc_coherent(struct device *hwdev, size_t size,
goto err_warn;

ret = phys_to_virt(paddr);
- dev_addr = phys_to_dma(hwdev, paddr);
+ dev_addr = swiotlb_phys_to_dma(hwdev, paddr);

/* Confirm address can be DMA'd by device */
if (dev_addr + size - 1 > dma_mask) {
@@ -758,15 +806,15 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
map = map_single(dev, phys, size, dir);
if (map == SWIOTLB_MAP_ERROR) {
swiotlb_full(dev, size, dir, 1);
- return phys_to_dma(dev, io_tlb_overflow_buffer);
+ return swiotlb_phys_to_dma(dev, io_tlb_overflow_buffer);
}

- dev_addr = phys_to_dma(dev, map);
+ dev_addr = swiotlb_phys_to_dma(dev, map);

/* Ensure that the address returned is DMA'ble */
if (!dma_capable(dev, dev_addr, size)) {
swiotlb_tbl_unmap_single(dev, map, size, dir);
- return phys_to_dma(dev, io_tlb_overflow_buffer);
+ return swiotlb_phys_to_dma(dev, io_tlb_overflow_buffer);
}

return dev_addr;
@@ -901,7 +949,7 @@ swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl, int nelems,
sg_dma_len(sgl) = 0;
return 0;
}
- sg->dma_address = phys_to_dma(hwdev, map);
+ sg->dma_address = swiotlb_phys_to_dma(hwdev, map);
} else
sg->dma_address = dev_addr;
sg_dma_len(sg) = sg->length;
@@ -985,7 +1033,7 @@ EXPORT_SYMBOL(swiotlb_sync_sg_for_device);
int
swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
{
- return (dma_addr == phys_to_dma(hwdev, io_tlb_overflow_buffer));
+ return (dma_addr == swiotlb_phys_to_dma(hwdev, io_tlb_overflow_buffer));
}
EXPORT_SYMBOL(swiotlb_dma_mapping_error);

@@ -998,6 +1046,6 @@ EXPORT_SYMBOL(swiotlb_dma_mapping_error);
int
swiotlb_dma_supported(struct device *hwdev, u64 mask)
{
- return phys_to_dma(hwdev, io_tlb_end - 1) <= mask;
+ return swiotlb_phys_to_dma(hwdev, io_tlb_end - 1) <= mask;
}
EXPORT_SYMBOL(swiotlb_dma_supported);