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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

# 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).

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);
+    }
+}
+
 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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