[PATCH v2 05/10] x86/tdx: Handle port I/O

From: Kuppuswamy Sathyanarayanan
Date: Sat Jun 26 2021 - 10:17:52 EST


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.

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 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 | 31 +++++++++++++++++++++++++++++++
2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 50f9eb17d364..b677f81168a0 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(PR_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(PR_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 a20bdbdc2bc8..ad035a5230e9 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -177,6 +177,34 @@ 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;
@@ -223,6 +251,9 @@ 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;
--
2.25.1