[PATCHv3 06/32] x86/tdx: Extend the confidential computing API to support TDX guests

[Kirill A. Shutemov]

Confidential Computing (CC) features (like string I/O unroll support,
memory encryption/decryption support, etc) are conditionally enabled
in the kernel using cc_platform_has() API. Since TDX guests also need
to use these CC features, extend cc_platform_has() API and add TDX
guest-specific CC attributes support.

Like AMD SME/SEV, TDX uses a bit in the page table entry to indicate
encryption status of the page, but the polarity of the mask is
opposite to AMD: if the bit is set the page is accessible to VMM.

Details about which bit in the page table entry to be used to indicate
shared/private state can be determined by using the TDINFO TDCALL.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 arch/x86/Kconfig              |  1 +
 arch/x86/coco/tdx.c           | 44 +++++++++++++++++++++++++++++++++++
 arch/x86/kernel/cc_platform.c |  6 +++++
 3 files changed, 51 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ea4190c53db6..581aaff0ccee 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -884,6 +884,7 @@ config INTEL_TDX_GUEST
 	bool "Intel TDX (Trust Domain Extensions) - Guest Support"
 	depends on X86_64 && CPU_SUP_INTEL
 	depends on X86_X2APIC
+	select ARCH_HAS_CC_PLATFORM
 	help
 	  Support running as a guest under Intel TDX.  Without this support,
 	  the guest kernel can not boot or run under TDX.
diff --git a/arch/x86/coco/tdx.c b/arch/x86/coco/tdx.c
index 89367fa576c1..87e561c5b4e3 100644
--- a/arch/x86/coco/tdx.c
+++ b/arch/x86/coco/tdx.c
@@ -5,8 +5,17 @@
 #define pr_fmt(fmt)     "tdx: " fmt
 
 #include <linux/cpufeature.h>
+#include <asm/coco.h>
 #include <asm/tdx.h>
 
+/* TDX module Call Leaf IDs */
+#define TDX_GET_INFO			1
+
+static struct {
+	unsigned int gpa_width;
+	unsigned long attributes;
+} td_info __ro_after_init;
+
 /*
  * Wrapper for standard use of __tdx_hypercall with no output aside from
  * return code.
@@ -25,9 +34,34 @@ static inline u64 _tdx_hypercall(u64 fn, u64 r12, u64 r13, u64 r14, u64 r15)
 	return __tdx_hypercall(&args, 0);
 }
 
+static inline void tdx_module_call(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
+				   struct tdx_module_output *out)
+{
+	if (__tdx_module_call(fn, rcx, rdx, r8, r9, out))
+		panic("TDCALL %lld failed (Buggy TDX module!)\n", fn);
+}
+
+static void get_info(void)
+{
+	struct tdx_module_output out;
+
+	/*
+	 * TDINFO TDX module call is used to get the TD execution environment
+	 * information like GPA width, number of available vcpus, debug mode
+	 * information, etc. More details about the ABI can be found in TDX
+	 * Guest-Host-Communication Interface (GHCI), section 2.4.2 TDCALL
+	 * [TDG.VP.INFO].
+	 */
+	tdx_module_call(TDX_GET_INFO, 0, 0, 0, 0, &out);
+
+	td_info.gpa_width = out.rcx & GENMASK(5, 0);
+	td_info.attributes = out.rdx;
+}
+
 void __init tdx_early_init(void)
 {
 	u32 eax, sig[3];
+	u64 mask;
 
 	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2],  &sig[1]);
 
@@ -36,5 +70,15 @@ void __init tdx_early_init(void)
 
 	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
 
+	get_info();
+
+	/*
+	 * The highest bit of a guest physical address is the "sharing" bit.
+	 * Set it for shared pages and clear it for private pages.
+	 */
+	mask = BIT_ULL(td_info.gpa_width - 1);
+
+	cc_init(CC_VENDOR_INTEL, mask);
+
 	pr_info("Guest detected\n");
 }
diff --git a/arch/x86/kernel/cc_platform.c b/arch/x86/kernel/cc_platform.c
index 93e6be7b7eca..dba713c444ab 100644
--- a/arch/x86/kernel/cc_platform.c
+++ b/arch/x86/kernel/cc_platform.c
@@ -90,6 +90,8 @@ u64 cc_get_mask(bool enc)
 	switch (cc_vendor) {
 	case CC_VENDOR_AMD:
 		return enc ? cc_mask : 0;
+	case CC_VENDOR_INTEL:
+		return enc ? 0 : cc_mask;
 	default:
 		return 0;
 	}
@@ -100,6 +102,8 @@ u64 cc_mkenc(u64 val)
 	switch (cc_vendor) {
 	case CC_VENDOR_AMD:
 		return val | cc_mask;
+	case CC_VENDOR_INTEL:
+		return val & ~cc_mask;
 	default:
 		return val;
 	}
@@ -110,6 +114,8 @@ u64 cc_mkdec(u64 val)
 	switch (cc_vendor) {
 	case CC_VENDOR_AMD:
 		return val & ~cc_mask;
+	case CC_VENDOR_INTEL:
+		return val | cc_mask;
 	default:
 		return val;
 	}
-- 
2.34.1