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To: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Maciej W. Rozycki" <macro@linux-mips.org>, David Fries <david@fries.net>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Fix i486 suspend to disk CR4 oops
From: Andi Kleen <andi@firstfloor.org>
References: <20080818040340.GB17528@spacedout.fries.net>
	<Pine.LNX.4.55.0808180510480.26857@cliff.in.clinika.pl>
	<48A8FC21.9060908@zytor.com>
Date: Mon, 18 Aug 2008 08:04:51 +0200
In-Reply-To: <48A8FC21.9060908@zytor.com> (H. Peter Anvin's message of "Sun, 17 Aug 2008 21:35:45 -0700")
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"H. Peter Anvin" <hpa@zytor.com> writes:

> 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.

Can be already checked for with boot_cpu_data.extended_cpuid_level.

-Andi