[PATCHv2 25/29] x86/kvm: Use bounce buffers for TD guest

Kirill A. Shutemov
2022-01-24T15:04:07Z

Intel TDX doesn't allow VMM to directly access guest private memory.
Any memory that is required for communication with the VMM must be
shared explicitly. The same rule applies for any DMA to and from the
TDX guest. All DMA pages have to be marked as shared pages. A generic way
to achieve this without any changes to device drivers is to use the
SWIOTLB framework.

Force SWIOTLB on TD guest and make SWIOTLB buffer shared by generalizing
mem_encrypt_init() to cover TDX.

Co-developed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/kernel/cc_platform.c | 1 +
arch/x86/kernel/tdx.c | 3 +++
arch/x86/mm/mem_encrypt.c | 9 ++++++++-
3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cc_platform.c b/arch/x86/kernel/cc_platform.c
index 1fbcf19fa20d..62c89c077cdd 100644
--- a/arch/x86/kernel/cc_platform.c
+++ b/arch/x86/kernel/cc_platform.c
@@ -23,6 +23,7 @@ static bool intel_cc_platform_has(enum cc_attr attr)
case CC_ATTR_HOTPLUG_DISABLED:
case CC_ATTR_GUEST_TDX:
case CC_ATTR_GUEST_MEM_ENCRYPT:
+ case CC_ATTR_MEM_ENCRYPT:
return true;
default:
return false;
diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index ea638c6ecb92..6048887ac846 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -5,6 +5,7 @@
#define pr_fmt(fmt) "tdx: " fmt

#include <linux/cpufeature.h>
+#include <linux/swiotlb.h>
#include <asm/tdx.h>
#include <asm/vmx.h>
#include <asm/insn.h>
@@ -581,5 +582,7 @@ void __init tdx_early_init(void)
*/
physical_mask &= GENMASK_ULL(td_info.gpa_width - 2, 0);

+ swiotlb_force = SWIOTLB_FORCE;
+
pr_info("Guest detected\n");
}
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index 50d209939c66..194ace3a748a 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -42,7 +42,14 @@ bool force_dma_unencrypted(struct device *dev)

static void print_mem_encrypt_feature_info(void)
{
- pr_info("AMD Memory Encryption Features active:");
+ pr_info("Memory Encryption Features active:");
+
+ if (cc_platform_has(CC_ATTR_GUEST_TDX)) {
+ pr_cont(" Intel TDX\n");
+ return;
+ }
+
+ pr_cont("AMD ");

/* Secure Memory Encryption */
if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT)) {
--
2.34.1