linux-kernel - [RFC v2-fix-v1 1/1] x86/tdx: Add helper to do MapGPA hypercall

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Date:   Wed, 26 May 2021 21:56:38 -0700
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: [RFC v2-fix-v1 1/1] x86/tdx: Add helper to do MapGPA hypercall

From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>

MapGPA hypercall is used by TDX guests to request VMM convert
the existing mapping of given GPA address range between
private/shared.

tdx_hcall_gpa_intent() is the wrapper used for making MapGPA
hypercall.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Reviewed-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
---

Changes since RFC v2:
  * Renamed tdg_map_gpa() to tdx_hcall_gpa_intent().
  * Fixed commit log and comments as per review comments.

 arch/x86/include/asm/tdx.h | 17 +++++++++++++++++
 arch/x86/kernel/tdx.c      | 24 ++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index a93528246595..eb9fa5f4d0e3 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -7,6 +7,15 @@
 
 #ifndef __ASSEMBLY__
 
+/*
+ * Page mapping type enum. This is software construct not
+ * part of any hardware or VMM ABI.
+ */
+enum tdx_map_type {
+	TDX_MAP_PRIVATE,
+	TDX_MAP_SHARED,
+};
+
 #ifdef CONFIG_INTEL_TDX_GUEST
 
 #include <asm/cpufeature.h>
@@ -119,6 +128,8 @@ do {									\
 #endif
 
 extern phys_addr_t tdg_shared_mask(void);
+extern int tdx_hcall_gpa_intent(phys_addr_t gpa, int numpages,
+				enum tdx_map_type map_type);
 
 #else // !CONFIG_INTEL_TDX_GUEST
 
@@ -143,6 +154,12 @@ static inline phys_addr_t tdg_shared_mask(void)
 {
 	return 0;
 }
+
+static inline int tdx_hcall_gpa_intent(phys_addr_t gpa, int numpages,
+				       enum tdx_map_type map_type)
+{
+	return -ENODEV;
+}
 #endif /* CONFIG_INTEL_TDX_GUEST */
 
 #ifdef CONFIG_INTEL_TDX_GUEST_KVM
diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index 0c8b10b78f32..a8ebd2d10093 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -16,6 +16,9 @@
 #define TDINFO				1
 #define TDGETVEINFO			3
 
+/* TDX hypercall Leaf IDs */
+#define TDVMCALL_MAP_GPA		0x10001
+
 #define VE_GET_IO_TYPE(exit_qual)      (((exit_qual) & 8) ? 0 : 1)
 #define VE_GET_IO_SIZE(exit_qual)      (((exit_qual) & 7) + 1)
 #define VE_GET_PORT_NUM(exit_qual)     ((exit_qual) >> 16)
@@ -122,6 +125,27 @@ static void tdg_get_info(void)
 	physical_mask &= ~tdg_shared_mask();
 }
 
+/*
+ * Inform the VMM of the guest's intent for this physical page:
+ * shared with the VMM or private to the guest.  The VMM is
+ * expected to change its mapping of the page in response.
+ *
+ * Note: shared->private conversions require further guest
+ * action to accept the page.
+ */
+int tdx_hcall_gpa_intent(phys_addr_t gpa, int numpages,
+			 enum tdx_map_type map_type)
+{
+	u64 ret;
+
+	if (map_type == TDX_MAP_SHARED)
+		gpa |= tdg_shared_mask();
+
+	ret = tdx_hypercall(TDVMCALL_MAP_GPA, gpa, PAGE_SIZE * numpages, 0, 0);
+
+	return ret ? -EIO : 0;
+}
+
 static __cpuidle void tdg_halt(void)
 {
 	u64 ret;
-- 
2.25.1