Re: 2.6.38.2 breaks suspend to disk

[Yinghai Lu <yinghai@kernel.org>]

On 04/01/2011 12:36 PM, H. Peter Anvin wrote:
> On 04/01/2011 12:32 PM, Yinghai Lu wrote:
>>
>> So for 32 bit, PAE support is not compiled in for old 486 cpus.
>> mmu_cr4_feautres will be used to make sure head_32.S will not access cr4.
>>
>> that could be the reason why 32 bit does not do read back at beginning.
>>
>
> Yes, but that doesn't explain why we shouldn't set new bits like NX and
> PSE in this register.

ok, please check if you are happy with this one.

From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

[PATCH -v3] x86: Save cr4 to mmu_cr4_features at boot time

Save cr4 to mmu_cr4_features at boot time

Michael reported 2.6.38.2 hibernation is broken by one backported patch.
it cause a freeze when resuming from hibernation

| "x86: Cleanup highmap after brk is concluded"
| commit id e5f15b45ddf3afa2bbbb10c7ea34fb32b6de0a0e.

it turns out the mmu_cr4 save it lost somehow.

-v3: read back cr4 for 32bit too according to HPA

Bisected-and-tested-by: Michael Leun <lkml20101129@newton.leun.net>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
  arch/x86/kernel/setup.c |   12 ++++++++++++
  1 file changed, 12 insertions(+)

Index: linux-2.6/arch/x86/kernel/setup.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/setup.c
+++ linux-2.6/arch/x86/kernel/setup.c
@@ -219,6 +219,17 @@ unsigned long mmu_cr4_features;
  unsigned long mmu_cr4_features = X86_CR4_PAE;
  #endif
  
+#if defined(CONFIG_X86_PAE) || defined(CONFIG_X86_64)
+static void __init read_back_mmu_cr4(void)
+{
+	mmu_cr4_features = read_cr4();
+}
+#else
+static void __init read_back_mmu_cr4(void)
+{
+}
+#endif
+
  /* Boot loader ID and version as integers, for the benefit of proc_dointvec */
  int bootloader_type, bootloader_version;
  
@@ -892,6 +903,7 @@ void __init setup_arch(char **cmdline_p)
  
  	high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
  #endif
+	read_back_mmu_cr4();
  
  	/*
  	 * Find and reserve possible boot-time SMP configuration: