Re: [Xen-devel] [PATCH 3 of 6] xen/pat: After suspend re-write PAT if BIOS changed it

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.03.12 at 18:41, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
> # HG changeset patch
> # User Simon Graham <simon.graham@xxxxxxxxxxxxxxxxxxx>
> # Date 1332610898 14400
> # Node ID 75798a472b1a9121adda166b6fd05ba8473a44f0
> # Parent  d097c3ba42f601af65b53a0c84973855aab64aa9
> xen/pat: After suspend re-write PAT if BIOS changed it.
> 
> Certain AMD machines (this was a MSI or GigaBYTE BIOS) after resume
> would reset the PAT MSR causing rather weird issues - where
> the pages would (say they would be set to WC) would end up with the
> wrong type (as they would use the BIOS PAT instead of the one set by
> the hypervisor).

There's a write of the PAT MSR already at the end of
restore_rest_processor_state() - are you saying this doesn't do
what is needed? Also note that this is properly gated by a check
of cpu_has_pat (other than the patch here does).

> Signed-off-by: Simon Graham <simon.graham@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> 
> diff -r d097c3ba42f6 -r 75798a472b1a xen/arch/x86/acpi/power.c
> --- a/xen/arch/x86/acpi/power.c       Sat Mar 24 12:54:12 2012 -0400
> +++ b/xen/arch/x86/acpi/power.c       Sat Mar 24 13:41:38 2012 -0400
> @@ -41,8 +41,25 @@ static DEFINE_SPINLOCK(pm_lock);
>  
>  struct acpi_sleep_info acpi_sinfo;
>  
> +static void pat_resume(void);
>  void do_suspend_lowlevel(void);
>  
> +static void
> +pat_resume()
> +{
> +    u64 pat;
> +
> +    rdmsrl(MSR_IA32_CR_PAT, pat);
> +    if (pat != host_pat) {
> +     printk(KERN_INFO PREFIX "Found PAT MSR: 0x%lx\n", pat);
> +     printk(KERN_INFO PREFIX "reseting to 0x%lx\n", host_pat);
> +     wrmsrl(MSR_IA32_CR_PAT, host_pat);
> +     rdmsrl(MSR_IA32_CR_PAT, pat);
> +     if (pat != host_pat)
> +         printk(KERN_WARNING PREFIX "PAT MSR stuck on: 0x%lx\n", pat);

All the %lx format specifiers here would break the 32-bit build afaict.
Further (if this code really is needed at all), please use %# instead
of 0x%.

Jan

> +    }
> +}
> +
>  static int device_power_down(void)
>  {
>      console_suspend();
> @@ -194,6 +211,7 @@ static int enter_state(u32 state)
>      if ( cpu_has_efer )
>          write_efer(read_efer());
>  
> +    pat_resume();
>      device_power_up();
>  
>      mcheck_init(&boot_cpu_data, 0);
> 
> 
> 
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> Xen-devel@xxxxxxxxxxxxx 
> http://lists.xen.org/xen-devel 




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