[PATCH 2/6] x86/tdx: Retry TDVMCALL_MAP_GPA() when needed

[Dexuan Cui <decui@microsoft.com>]

GHCI spec for TDX 1.0 says that the MapGPA call may fail with the R10
error code = TDG.VP.VMCALL_RETRY (1), and the guest must retry this
operation for the pages in the region starting at the GPA specified
in R11.

When a TDX guest runs on Hyper-V, Hyper-V returns the retry error
when hyperv_init() -> swiotlb_update_mem_attributes() ->
set_memory_decrypted() decrypts up to 1GB of swiotlb bounce buffers.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
---
 arch/x86/coco/tdx/tdx.c | 65 +++++++++++++++++++++++++++++++++++++----
 1 file changed, 59 insertions(+), 6 deletions(-)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 3fee96931ff5..46971cc7d006 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -20,6 +20,8 @@
 /* TDX hypercall Leaf IDs */
 #define TDVMCALL_MAP_GPA		0x10001
 
+#define TDVMCALL_STATUS_RETRY		1
+
 /* MMIO direction */
 #define EPT_READ	0
 #define EPT_WRITE	1
@@ -52,6 +54,25 @@ static inline u64 _tdx_hypercall(u64 fn, u64 r12, u64 r13, u64 r14, u64 r15)
 	return __tdx_hypercall(&args, 0);
 }
 
+static inline u64 _tdx_hypercall_output_r11(u64 fn, u64 r12, u64 r13, u64 r14,
+					    u64 r15, u64 *r11)
+{
+	struct tdx_hypercall_args args = {
+		.r10 = TDX_HYPERCALL_STANDARD,
+		.r11 = fn,
+		.r12 = r12,
+		.r13 = r13,
+		.r14 = r14,
+		.r15 = r15,
+	};
+
+	u64 ret;
+
+	ret = __tdx_hypercall(&args, TDX_HCALL_HAS_OUTPUT);
+	*r11 = args.r11;
+	return ret;
+}
+
 /* Called from __tdx_hypercall() for unrecoverable failure */
 void __tdx_hypercall_failed(void)
 {
@@ -691,6 +712,43 @@ static bool try_accept_one(phys_addr_t *start, unsigned long len,
 	return true;
 }
 
+/*
+ * Notify the VMM about page mapping conversion. More info about ABI
+ * can be found in TDX Guest-Host-Communication Interface (GHCI),
+ * section "TDG.VP.VMCALL<MapGPA>"
+ */
+static bool tdx_map_gpa(phys_addr_t start, phys_addr_t end, bool enc)
+{
+	u64 ret, r11;
+
+	while (1) {
+		ret = _tdx_hypercall_output_r11(TDVMCALL_MAP_GPA, start,
+						end - start, 0, 0, &r11);
+		if (!ret)
+			break;
+
+		if (ret != TDVMCALL_STATUS_RETRY)
+			break;
+
+		/*
+		 * The guest must retry the operation for the pages in the
+		 * region starting at the GPA specified in R11. Make sure R11
+		 * contains a sane value.
+		 */
+		if ((r11 & ~cc_mkdec(0)) < (start & ~cc_mkdec(0)) ||
+		    (r11 & ~cc_mkdec(0)) >= (end  & ~cc_mkdec(0)))
+			return false;
+
+		start = r11;
+
+		/* Set the shared (decrypted) bit. */
+		if (!enc)
+			start |= cc_mkdec(0);
+	}
+
+	return !ret;
+}
+
 /*
  * 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
@@ -707,12 +765,7 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
 		end   |= cc_mkdec(0);
 	}
 
-	/*
-	 * Notify the VMM about page mapping conversion. More info about ABI
-	 * can be found in TDX Guest-Host-Communication Interface (GHCI),
-	 * section "TDG.VP.VMCALL<MapGPA>"
-	 */
-	if (_tdx_hypercall(TDVMCALL_MAP_GPA, start, end - start, 0, 0))
+	if (!tdx_map_gpa(start, end, enc))
 		return false;
 
 	/* private->shared conversion  requires only MapGPA call */
-- 
2.25.1