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SubjectRe: [PATCH] Fix i486 suspend to disk CR4 oops
Maciej W. Rozycki wrote:
> On Sun, 17 Aug 2008, David Fries wrote:
>
>> arch/x86/power/cpu_32.c __save_processor_state calls read_cr4()
>> only a i486 CPU doesn't have the CR4 register. Trying to read it
>> produces an invalid opcode oops during suspend to disk.
> [...]
>> diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
>> index 81e5ab6..bd0f2a3 100644
>> --- a/arch/x86/kernel/acpi/sleep.c
>> +++ b/arch/x86/kernel/acpi/sleep.c
>> @@ -86,7 +86,9 @@ int acpi_save_state_mem(void)
>> #endif /* !CONFIG_64BIT */
>>
>> header->pmode_cr0 = read_cr0();
>> - header->pmode_cr4 = read_cr4();
>> + /* cr4 was introduced in the Pentium CPU */
>> + if (boot_cpu_data.x86 >= 5)
>> + header->pmode_cr4 = read_cr4();
>> header->realmode_flags = acpi_realmode_flags;
>> header->real_magic = 0x12345678;
>>
>
> NACK. Later i486 chips do have CR4 -- for PSE, VME, etc. (the set of
> features varies across the line). Use a fixup as elsewhere or something.
>

The other alternative is to probe for the CPUID instruction (via
EFLAGS.ID) -- CR4 is present if and only if CPUID exists.

-hpa


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