[PATCHv4 27/30] x86/kvm: Use bounce buffers for TD guest

Kirill A. Shutemov
2022-02-24T15:58:01Z

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/Kconfig | 2 +-
arch/x86/coco/core.c | 1 +
arch/x86/coco/tdx.c | 3 +++
arch/x86/mm/mem_encrypt.c | 9 ++++++++-
4 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 98efb35ed7b1..1312cefb927d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -885,7 +885,7 @@ config INTEL_TDX_GUEST
depends on X86_64 && CPU_SUP_INTEL
depends on X86_X2APIC
select ARCH_HAS_CC_PLATFORM
- select DYNAMIC_PHYSICAL_MASK
+ select X86_MEM_ENCRYPT
select X86_MCE
help
Support running as a guest under Intel TDX. Without this support,
diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c
index 9778cf4c6901..b10326f91d4f 100644
--- a/arch/x86/coco/core.c
+++ b/arch/x86/coco/core.c
@@ -22,6 +22,7 @@ static bool intel_cc_platform_has(enum cc_attr attr)
case CC_ATTR_GUEST_UNROLL_STRING_IO:
case CC_ATTR_HOTPLUG_DISABLED:
case CC_ATTR_GUEST_MEM_ENCRYPT:
+ case CC_ATTR_MEM_ENCRYPT:
return true;
default:
return false;
diff --git a/arch/x86/coco/tdx.c b/arch/x86/coco/tdx.c
index da2ae399ea71..d33f65a58d7b 100644
--- a/arch/x86/coco/tdx.c
+++ b/arch/x86/coco/tdx.c
@@ -5,6 +5,7 @@
#define pr_fmt(fmt) "tdx: " fmt

#include <linux/cpufeature.h>
+#include <linux/swiotlb.h>
#include <asm/coco.h>
#include <asm/tdx.h>
#include <asm/vmx.h>
@@ -587,5 +588,7 @@ void __init tdx_early_init(void)
x86_platform.guest.enc_tlb_flush_required = tdx_tlb_flush_required;
x86_platform.guest.enc_status_change_finish = tdx_enc_status_changed;

+ 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..10ee40b5204b 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 (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
+ pr_cont(" Intel TDX\n");
+ return;
+ }
+
+ pr_cont("AMD ");

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