[PATCH] Feature: Expose x86 CPU FMS from cpuid module

* [PATCH] Feature: Expose x86 CPU FMS from cpuid module
@ 2023-04-12  9:40 Paterson, Harley
  2024-03-07 14:43 ` Herrenschmidt, Benjamin via Grub-devel
  0 siblings, 1 reply; 2+ messages in thread
From: Paterson, Harley @ 2023-04-12  9:40 UTC (permalink / raw)
  To: grub-devel@gnu.org; +Cc: Herrenschmidt, Benjamin

This patch exposes an x86 CPU's model, family, and stepping via flag in
the `cpuid` command.

Invoking `cpuid -f` will set the Grub environment variables
`CPUID_FAMILY`, `CPUID_MODEL`, and `CPUID_STEP` for consumption by Grub
scripts.

Accessing the CPU FMS data requires a `cpuid(0x1)` call on both x86 and
x64 systems. Calling `cpuid(0x1)` first requires checking `cpuid` can be
called on the processor, and then checking the maximum parameter
accepted by the CPU's `cpuid` implementation is greater than or equal to
one.

The x86 implementation of this code already has these checks (and calls
`cpuid(0x1)`) to discover the presence of long mode and PAE. These
features are currently assumed to be present on x64.

This patch runs the tests on both x86 and x86_64.  This existing shortcut
saves trivial time, but we would need the same code paths for
the FMS anyway - better always run the PAE tests too,
rather than duplicate the code minus these fast tests (bitshifts and
xors).

The CPU FMS format is common across both AMD and Intel devices. The long
mode flags bit is undefined in x64. The long-mode check is disabled
on x64 and assumed true, consistent with existing behaviour. See:

* https://www.amd.com/system/files/TechDocs/25481.pdf
* https://www.scss.tcd.ie/~jones/CS4021/processor-identification-cpuid-instruction-note.pdf
---
 grub-core/commands/i386/cpuid.c | 73 ++++++++++++++++++++++++++++-----
 1 file changed, 62 insertions(+), 11 deletions(-)

diff --git a/grub-core/commands/i386/cpuid.c b/grub-core/commands/i386/cpuid.c
index 42b9841..90d857b 100644
--- a/grub-core/commands/i386/cpuid.c
+++ b/grub-core/commands/i386/cpuid.c
@@ -35,13 +35,15 @@ static const struct grub_arg_option options[] =
        no argument is specified.  */
     {"long-mode", 'l', 0, N_("Check if CPU supports 64-bit (long) mode (default)."), 0, 0},
     {"pae", 'p', 0, N_("Check if CPU supports Physical Address Extension."), 0, 0},
+    {"fms", 'f', 0, "Set CPUID_FAMILY, CPUID_MODEL, and CPUID_STEP variables.", 0, 0},
     {0, 0, 0, 0, 0, 0}
   };
 
 enum
   {
     MODE_LM = 0,
-    MODE_PAE = 1
+    MODE_PAE = 1,
+    MODE_FMS = 2
   };
 
 enum
@@ -52,8 +54,45 @@ enum
   {
     bit_LM = (1 << 29)
   };
+enum
+  {
+    /* 8 bit number (3 base 10 digits) plus terminator. */
+    FMS_BUF_LEN = 4,
+  };
+
+unsigned char grub_cpuid_has_longmode = 0;
+unsigned char grub_cpuid_has_pae = 0;
+int grub_cpuid_family = -1;
+int grub_cpuid_model = -1;
+int grub_cpuid_step = -1;
 
-unsigned char grub_cpuid_has_longmode = 0, grub_cpuid_has_pae = 0;
+
+static void
+set_cpuid_env(void)
+{
+  char fms[FMS_BUF_LEN] = {0};
+  if (grub_cpuid_family != -1)
+  {
+    grub_snprintf(fms, FMS_BUF_LEN - 1, "%d", grub_cpuid_family);
+    grub_env_set("CPUID_FAMILY", fms);
+  }
+  else
+    grub_env_set("CPUID_FAMILY", "unknown");
+  if (grub_cpuid_model != -1)
+  {
+    grub_snprintf(fms, FMS_BUF_LEN - 1, "%d", grub_cpuid_model);
+    grub_env_set("CPUID_MODEL", fms);
+  }
+  else
+    grub_env_set("CPUID_MODEL", "unknown");
+  if (grub_cpuid_step != -1)
+  {
+    grub_snprintf(fms, FMS_BUF_LEN - 1, "%d", grub_cpuid_step);
+    grub_env_set("CPUID_STEP", fms);
+  }
+  else
+    grub_env_set("CPUID_STEP", "unknown");
+}
 
 static grub_err_t
 grub_cmd_cpuid (grub_extcmd_context_t ctxt,
@@ -61,7 +100,12 @@ grub_cmd_cpuid (grub_extcmd_context_t ctxt,
 		char **args __attribute__ ((unused)))
 {
   int val = 0;
-  if (ctxt->state[MODE_PAE].set)
+  if (ctxt->state[MODE_FMS].set)
+  {
+    set_cpuid_env();
+    return GRUB_ERR_NONE;
+  }
+  else if (ctxt->state[MODE_PAE].set)
     val = grub_cpuid_has_pae;
   else
     val = grub_cpuid_has_longmode;
@@ -75,20 +119,24 @@ static grub_extcmd_t cmd;
 
 GRUB_MOD_INIT(cpuid)
 {
-#ifdef __x86_64__
-  /* grub-emu */
-  grub_cpuid_has_longmode = 1;
-  grub_cpuid_has_pae = 1;
-#else
-  unsigned int eax, ebx, ecx, edx;
   unsigned int max_level;
   unsigned int ext_level;
 
   /* See if we can use cpuid.  */
+#ifdef __x86_64__
+  unsigned long eax, ebx, ecx, edx;
+  grub_cpuid_has_longmode = 1;
+  asm volatile ("pushf; pushf; pop %0; mov %0,%1; xor %2,%0;"
+		"push %0; popf; pushf; pop %0; popf"
+		: "=&r" (eax), "=&r" (ebx)
+		: "i" (0x00200000));
+#else
+  unsigned int eax, ebx, ecx, edx;
   asm volatile ("pushfl; pushfl; popl %0; movl %0,%1; xorl %2,%0;"
 		"pushl %0; popfl; pushfl; popl %0; popfl"
 		: "=&r" (eax), "=&r" (ebx)
 		: "i" (0x00200000));
+#endif
   if (((eax ^ ebx) & 0x00200000) == 0)
     goto done;
 
@@ -103,8 +151,12 @@ GRUB_MOD_INIT(cpuid)
     {
       grub_cpuid (1, eax, ebx, ecx, edx);
       grub_cpuid_has_pae = !!(edx & bit_PAE);
+      grub_cpuid_step = eax & 0xf;
+      grub_cpuid_model = ((eax >> 4) & 0xf) + (((eax >> 16) & 0xf) << 4);
+      grub_cpuid_family = ((eax >> 8) & 0xf) + ((eax >> 20) & 0xff);
     }
 
+#ifndef __x86_64__
   grub_cpuid (0x80000000, eax, ebx, ecx, edx);
   ext_level = eax;
   if (ext_level < 0x80000000)
@@ -112,9 +164,8 @@ GRUB_MOD_INIT(cpuid)
 
   grub_cpuid (0x80000001, eax, ebx, ecx, edx);
   grub_cpuid_has_longmode = !!(edx & bit_LM);
-done:
 #endif
-
+done:
   cmd = grub_register_extcmd ("cpuid", grub_cmd_cpuid, 0,
 			      "[-l]", N_("Check for CPU features."), options);
 }
-- 
2.39.2



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