[PATCH v7 05/10] x86/tdx: Handle port I/O

Kuppuswamy Sathyanarayanan
2021-10-05T20:42:16Z

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

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 confidential guest flag CC_ATTR_GUEST_UNROLL_STRING_IO to
add string unroll support in asm/io.h

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

Changes since v6:
* None

Changes since v5:
* Changed prot_guest_has() to cc_platform_has().

Changes since v4:
* Changed order of variable declaration in tdx_handle_io().
* Changed tdg_* prefix with tdx_*.

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/cpu/intel.c | 1 +
arch/x86/kernel/tdx.c | 35 +++++++++++++++++++++++++++++++++++
include/linux/cc_platform.h | 11 +++++++++++
4 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index fa6aa43e5dc3..67e0c4a0a0f4 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/cc_platform.h>
#include <asm/page.h>
#include <asm/tdx.h>
#include <asm/early_ioremap.h>
@@ -310,7 +311,8 @@ 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() || \
+ cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO)) { \
unsigned type *value = (unsigned type *)addr; \
while (count) { \
out##bwl(*value, port); \
@@ -326,7 +328,8 @@ 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() || \
+ cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO)) { \
unsigned type *value = (unsigned type *)addr; \
while (count) { \
*value = in##bwl(port); \
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index b99ead877549..01d7935feaed 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -67,6 +67,7 @@ bool intel_cc_platform_has(enum cc_attr attr)
{
switch (attr) {
case CC_ATTR_GUEST_TDX:
+ case CC_ATTR_GUEST_UNROLL_STRING_IO:
return is_tdx_guest;
default:
return false;
diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index 4cbffcb737d9..cd0fb5d14ad7 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -175,6 +175,38 @@ static u64 tdx_handle_cpuid(struct pt_regs *regs)
return ret;
}

+/*
+ * 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,
+ * tdx_handle_io() will be extended to use trace calls which is also
+ * not valid for early I/O cases.
+ */
+static void tdx_handle_io(struct pt_regs *regs, u32 exit_qual)
+{
+ struct tdx_hypercall_output outh;
+ int out, size, port, ret;
+ bool string;
+ u64 mask;
+
+ string = VE_IS_IO_STRING(exit_qual);
+
+ /* I/O strings ops are unrolled at build time. */
+ BUG_ON(string);
+
+ out = VE_IS_IO_OUT(exit_qual);
+ size = VE_GET_IO_SIZE(exit_qual);
+ port = VE_GET_PORT_NUM(exit_qual);
+ mask = GENMASK(8 * size, 0);
+
+ 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 tdx_get_ve_info(struct ve_info *ve)
{
struct tdx_module_output out = {0};
@@ -221,6 +253,9 @@ int tdx_handle_virtualization_exception(struct pt_regs *regs,
case EXIT_REASON_CPUID:
ret = tdx_handle_cpuid(regs);
break;
+ case EXIT_REASON_IO_INSTRUCTION:
+ tdx_handle_io(regs, ve->exit_qual);
+ break;
default:
pr_warn("Unexpected #VE: %lld\n", ve->exit_reason);
return -EFAULT;
diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
index 26eb19f37d56..03dfddd736d2 100644
--- a/include/linux/cc_platform.h
+++ b/include/linux/cc_platform.h
@@ -70,6 +70,17 @@ enum cc_attr {
* Examples include Intel TDX.
*/
CC_ATTR_GUEST_TDX,
+
+ /**
+ * @CC_ATTR_GUEST_UNROLL_STRING_IO: String I/O is implemented with
+ * IN/OUT instructions
+ *
+ * The platform/OS is running as a guest/virtual machine and uses
+ * IN/OUT instructions in place of string I/O.
+ *
+ * Examples include TDX Guest.
+ */
+ CC_ATTR_GUEST_UNROLL_STRING_IO,
};

#ifdef CONFIG_ARCH_HAS_CC_PLATFORM
--
2.25.1