[GRUB PATCH RFC 03/18] i386/msr: Extract and improve MSR support detection code

[Daniel Kiper]

Currently rdmsr and wrmsr commands have own MSR support detection code.
This code is the same. So, it is duplicated. Additionally, this code
cannot be reused by others. Hence, extract this code to a function and
make it public. By the way, improve a code a bit.

Additionally, use GRUB_ERR_BAD_DEVICE instead of GRUB_ERR_BUG to signal
an error because errors encountered by this new routine are not bugs.

Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
---
 grub-core/commands/i386/rdmsr.c | 21 +++++----------------
 grub-core/commands/i386/wrmsr.c | 21 +++++----------------
 include/grub/i386/msr.h         | 29 +++++++++++++++++++++++++++++
 3 files changed, 39 insertions(+), 32 deletions(-)

diff --git a/grub-core/commands/i386/rdmsr.c b/grub-core/commands/i386/rdmsr.c
index 89ece7657..2e42f6197 100644
--- a/grub-core/commands/i386/rdmsr.c
+++ b/grub-core/commands/i386/rdmsr.c
@@ -42,27 +42,16 @@ static const struct grub_arg_option options[] =
 static grub_err_t
 grub_cmd_msr_read (grub_extcmd_context_t ctxt, int argc, char **argv)
 {
-  grub_uint32_t manufacturer[3], max_cpuid, a, b, c, features, addr;
+  grub_err_t err;
+  grub_uint32_t addr;
   grub_uint64_t value;
   const char *ptr;
   char buf[sizeof("1122334455667788")];
 
-  /*
-   * The CPUID instruction should be used to determine whether MSRs
-   * are supported. (CPUID.01H:EDX[5] = 1)
-   */
-  if (! grub_cpu_is_cpuid_supported ())
-    return grub_error (GRUB_ERR_BUG, N_("unsupported instruction"));
+  err = grub_cpu_is_msr_supported ();
 
-  grub_cpuid (0, max_cpuid, manufacturer[0], manufacturer[2], manufacturer[1]);
-
-  if (max_cpuid < 1)
-    return grub_error (GRUB_ERR_BUG, N_("unsupported instruction"));
-
-  grub_cpuid (1, a, b, c, features);
-
-  if (!(features & (1 << 5)))
-    return grub_error (GRUB_ERR_BUG, N_("unsupported instruction"));
+  if (err != GRUB_ERR_NONE)
+    return grub_error (err, N_("RDMSR is unsupported"));
 
   if (argc != 1)
     return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("one argument expected"));
diff --git a/grub-core/commands/i386/wrmsr.c b/grub-core/commands/i386/wrmsr.c
index e3e9f2ee3..d14bb3176 100644
--- a/grub-core/commands/i386/wrmsr.c
+++ b/grub-core/commands/i386/wrmsr.c
@@ -35,26 +35,15 @@ static grub_command_t cmd_write;
 static grub_err_t
 grub_cmd_msr_write (grub_command_t cmd __attribute__ ((unused)), int argc, char **argv)
 {
-  grub_uint32_t manufacturer[3], max_cpuid, a, b, c, features, addr;
+  grub_err_t err;
+  grub_uint32_t addr;
   grub_uint64_t value;
   const char *ptr;
 
-  /*
-   * The CPUID instruction should be used to determine whether MSRs
-   * are supported. (CPUID.01H:EDX[5] = 1)
-   */
-  if (!grub_cpu_is_cpuid_supported ())
-    return grub_error (GRUB_ERR_BUG, N_("unsupported instruction"));
+  err = grub_cpu_is_msr_supported ();
 
-  grub_cpuid (0, max_cpuid, manufacturer[0], manufacturer[2], manufacturer[1]);
-
-  if (max_cpuid < 1)
-    return grub_error (GRUB_ERR_BUG, N_("unsupported instruction"));
-
-  grub_cpuid (1, a, b, c, features);
-
-  if (!(features & (1 << 5)))
-    return grub_error (GRUB_ERR_BUG, N_("unsupported instruction"));
+  if (err != GRUB_ERR_NONE)
+    return grub_error (err, N_("WRMSR is unsupported"));
 
   if (argc != 2)
     return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("two arguments expected"));
diff --git a/include/grub/i386/msr.h b/include/grub/i386/msr.h
index 4fba1b8e0..1e838c022 100644
--- a/include/grub/i386/msr.h
+++ b/include/grub/i386/msr.h
@@ -19,6 +19,35 @@
 #ifndef GRUB_I386_MSR_H
 #define GRUB_I386_MSR_H 1
 
+#include <grub/err.h>
+#include <grub/i386/cpuid.h>
+#include <grub/types.h>
+
+static inline grub_err_t
+grub_cpu_is_msr_supported (void)
+{
+  grub_uint32_t eax, ebx, ecx, edx;
+
+  /*
+   * The CPUID instruction should be used to determine whether MSRs
+   * are supported, CPUID.01H:EDX[5] = 1.
+   */
+  if (!grub_cpu_is_cpuid_supported ())
+    return GRUB_ERR_BAD_DEVICE;
+
+  grub_cpuid (0, eax, ebx, ecx, edx);
+
+  if (eax < 1)
+    return GRUB_ERR_BAD_DEVICE;
+
+  grub_cpuid (1, eax, ebx, ecx, edx);
+
+  if (!(edx & (1 << 5)))
+    return GRUB_ERR_BAD_DEVICE;
+
+  return GRUB_ERR_NONE;
+}
+
 /*
  * TODO: Add a general protection exception handler.
  *       Accessing a reserved or unimplemented MSR address results in a GP#.
-- 
2.11.0