Re: [PATCH v10 10/12] x86, mm, pat: Cleanup init flags in pat_init()

[Borislav Petkov]

On Wed, May 27, 2015 at 09:19:02AM -0600, Toshi Kani wrote:
> pat_init() uses two flags, 'boot_cpu' and 'boot_pat_state', for
> tracking the boot CPU's initialization status.  'boot_pat_state'
> is also overloaded to carry the boot PAT value.
> 
> This patch cleans this up by replacing them with a new single
> flag, 'boot_cpu_done', to track the boot CPU's initialization
> status.  'boot_pat_state' is only used to carry the boot PAT
> value as a result.
> 
> Suggested-by: Thomas Gleixner 
> Signed-off-by: Toshi Kani 
> ---
>  arch/x86/mm/pat.c |   42 --
>  1 file changed, 20 insertions(+), 22 deletions(-)

...

> + rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
> + if (!boot_pat_state) {
> + pat_disable("PAT read returns always zero, disabled.");
> + return;
> + }
> + } else if (!cpu_has_pat) {
> + /*
> +  * If this happens we are on a secondary CPU, but
> +  * switched to PAT on the boot CPU. We have no way to
> +  * undo PAT.
> +  */
> + pr_err("PAT enabled, but not supported by secondary CPU\n");
> + BUG();

These could be replaced with a panic().

-- 
Regards/Gruss,
Boris.

ECO tip #101: Trim your mails when you reply.
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[PATCH v10 10/12] x86, mm, pat: Cleanup init flags in pat_init()

[Toshi Kani]

pat_init() uses two flags, 'boot_cpu' and 'boot_pat_state', for
tracking the boot CPU's initialization status.  'boot_pat_state'
is also overloaded to carry the boot PAT value.

This patch cleans this up by replacing them with a new single
flag, 'boot_cpu_done', to track the boot CPU's initialization
status.  'boot_pat_state' is only used to carry the boot PAT
value as a result.

Suggested-by: Thomas Gleixner 
Signed-off-by: Toshi Kani 
---
 arch/x86/mm/pat.c |   42 --
 1 file changed, 20 insertions(+), 22 deletions(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 92fc635..7cfd995 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -201,26 +201,31 @@ void pat_init_cache_modes(void)
 void pat_init(void)
 {
u64 pat;
-   bool boot_cpu = !boot_pat_state;
struct cpuinfo_x86 *c = &boot_cpu_data;
+   static bool boot_cpu_done;
 
if (!pat_enabled)
return;
 
-   if (!cpu_has_pat) {
-   if (!boot_pat_state) {
+   if (!boot_cpu_done) {
+   if (!cpu_has_pat) {
pat_disable("PAT not supported by CPU.");
return;
-   } else {
-   /*
-* If this happens we are on a secondary CPU, but
-* switched to PAT on the boot CPU. We have no way to
-* undo PAT.
-*/
-   printk(KERN_ERR "PAT enabled, "
-  "but not supported by secondary CPU\n");
-   BUG();
}
+
+   rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
+   if (!boot_pat_state) {
+   pat_disable("PAT read returns always zero, disabled.");
+   return;
+   }
+   } else if (!cpu_has_pat) {
+   /*
+* If this happens we are on a secondary CPU, but
+* switched to PAT on the boot CPU. We have no way to
+* undo PAT.
+*/
+   pr_err("PAT enabled, but not supported by secondary CPU\n");
+   BUG();
}
 
if ((c->x86_vendor == X86_VENDOR_INTEL) &&
@@ -279,19 +284,12 @@ void pat_init(void)
  PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, WT);
}
 
-   /* Boot CPU check */
-   if (!boot_pat_state) {
-   rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
-   if (!boot_pat_state) {
-   pat_disable("PAT read returns always zero, disabled.");
-   return;
-   }
-   }
-
wrmsrl(MSR_IA32_CR_PAT, pat);
 
-   if (boot_cpu)
+   if (!boot_cpu_done) {
pat_init_cache_modes();
+   boot_cpu_done = true;
+   }
 }
 
 #undef PAT
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