[PATCH v4 05/10] x86/tdx: Handle port I/O

[Kuppuswamy Sathyanarayanan]

From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>

TDX hypervisors cannot emulate instructions directly. This
includes port IO which is normally emulated in the hypervisor.
All port IO instructions inside TDX trigger the #VE exception
in the guest and would be normally emulated there.

Also string I/O is not supported in TDX guest. So, unroll the
string I/O operation into a loop operating on one element at
a time. This method is similar to AMD SEV, so just extend the
support for TDX guest platform.

Add a new protected guest flag PATTR_GUEST_UNROLL_STRING_IO
to add string unroll support in asm/io.h

Co-developed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---

Changes since v3:
 * Included PATTR_GUEST_UNROLL_STRING_IO protected guest flag
   addition change in this patch.
 * Rebased on top of Tom Lendacks protected guest change.

Changes since v2:
 * None

Changes since v1:
 * Fixed comments for tdg_handle_io().
 * Used _tdx_hypercall() instead of __tdx_hypercall() in tdg_handle_io().

 arch/x86/include/asm/io.h       |  7 +++++--
 arch/x86/kernel/tdx.c           | 32 ++++++++++++++++++++++++++++++++
 include/linux/protected_guest.h |  1 +
 3 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 50f9eb17d364..4c9e06a81ebe 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -40,6 +40,7 @@
 
 #include <linux/string.h>
 #include <linux/compiler.h>
+#include <linux/protected_guest.h>
 #include <asm/page.h>
 #include <asm/early_ioremap.h>
 #include <asm/pgtable_types.h>
@@ -309,7 +310,8 @@ static inline unsigned type in##bwl##_p(int port)			\
 									\
 static inline void outs##bwl(int port, const void *addr, unsigned long count) \
 {									\
-	if (sev_key_active()) {						\
+	if (sev_key_active() ||						\
+	    prot_guest_has(PATTR_GUEST_UNROLL_STRING_IO)) {		\
 		unsigned type *value = (unsigned type *)addr;		\
 		while (count) {						\
 			out##bwl(*value, port);				\
@@ -325,7 +327,8 @@ static inline void outs##bwl(int port, const void *addr, unsigned long count) \
 									\
 static inline void ins##bwl(int port, void *addr, unsigned long count)	\
 {									\
-	if (sev_key_active()) {						\
+	if (sev_key_active() ||						\
+	    prot_guest_has(PATTR_GUEST_UNROLL_STRING_IO)) {		\
 		unsigned type *value = (unsigned type *)addr;		\
 		while (count) {						\
 			*value = in##bwl(port);				\
diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index b9a66f8de5e5..c6dd7960fd2b 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -62,6 +62,7 @@ bool tdx_prot_guest_has(unsigned long flag)
 {
 	switch (flag) {
 	case PATTR_GUEST_TDX:
+	case PATTR_GUEST_UNROLL_STRING_IO:
 		return cpu_feature_enabled(X86_FEATURE_TDX_GUEST);
 	}
 
@@ -173,6 +174,34 @@ static void tdg_handle_cpuid(struct pt_regs *regs)
 	regs->dx = out.r15;
 }
 
+/*
+ * tdx_handle_early_io() cannot be re-used in #VE handler for handling
+ * I/O because the way of handling string I/O is different between
+ * normal and early I/O case. Also, once trace support is enabled,
+ * tdg_handle_io() will be extended to use trace calls which is also
+ * not valid for early I/O cases.
+ */
+static void tdg_handle_io(struct pt_regs *regs, u32 exit_qual)
+{
+	struct tdx_hypercall_output outh;
+	int out = VE_IS_IO_OUT(exit_qual);
+	int size = VE_GET_IO_SIZE(exit_qual);
+	int port = VE_GET_PORT_NUM(exit_qual);
+	u64 mask = GENMASK(8 * size, 0);
+	bool string = VE_IS_IO_STRING(exit_qual);
+	int ret;
+
+	/* I/O strings ops are unrolled at build time. */
+	BUG_ON(string);
+
+	ret = _tdx_hypercall(EXIT_REASON_IO_INSTRUCTION, size, out, port,
+			     regs->ax, &outh);
+	if (!out) {
+		regs->ax &= ~mask;
+		regs->ax |= (ret ? UINT_MAX : outh.r11) & mask;
+	}
+}
+
 unsigned long tdg_get_ve_info(struct ve_info *ve)
 {
 	u64 ret;
@@ -219,6 +248,9 @@ int tdg_handle_virtualization_exception(struct pt_regs *regs,
 	case EXIT_REASON_CPUID:
 		tdg_handle_cpuid(regs);
 		break;
+	case EXIT_REASON_IO_INSTRUCTION:
+		tdg_handle_io(regs, ve->exit_qual);
+		break;
 	default:
 		pr_warn("Unexpected #VE: %lld\n", ve->exit_reason);
 		return -EFAULT;
diff --git a/include/linux/protected_guest.h b/include/linux/protected_guest.h
index 9085f5dd834c..1a350c3fcfe2 100644
--- a/include/linux/protected_guest.h
+++ b/include/linux/protected_guest.h
@@ -16,6 +16,7 @@
 #define PATTR_HOST_MEM_ENCRYPT		1	/* Host encrypted memory */
 #define PATTR_GUEST_MEM_ENCRYPT		2	/* Guest encrypted memory */
 #define PATTR_GUEST_PROT_STATE		3	/* Guest encrypted state */
+#define PATTR_GUEST_UNROLL_STRING_IO	4	/* Unrolled string IO */
 
 /* 0x800 - 0x8ff reserved for AMD */
 #define PATTR_SME			0x800
-- 
2.25.1