Re: [PATCH 3/3] x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LMCPUID bit

From: H. Peter Anvin
Date: Sun Aug 30 2009 - 16:03:01 EST

On 08/30/2009 12:30 PM, Borislav Petkov wrote:
> On Sun, Aug 30, 2009 at 12:22:34PM -0700, H. Peter Anvin wrote:
>> On 08/30/2009 04:50 AM, Borislav Petkov wrote:
>>> clear_cpu_cap(c, X86_FEATURE_LAHF_LM);
>>> + if (!rdmsrl_amd_safe(0xc001100d, &val)) {
>>> + val &= ~(1ULL << 32);
>>> + wrmsr_amd_safe(0xc001100d, (u32) val,
>>> + (u32)(val >> 32));
>>> + }
>>> + }
>> We presumably want/need wrmsrl_amd_safe() here!
> Actually, it is wrmsr_amd_safe() because we need the magic value in
> %edi. wrmsr_amd_safe() calls the _regs variant with the array argument.
> And we don't have a wrmsrl_amd_safe-one which gets a 64bit msr value as
> an argument similar to the rdmsrl one.

That's exactly the point. We shouldn't have rdmsrl_amd_safe() on one
hand and wrmsr_asm_safe() on the other. I have already fixed this up in
my tree, but this kind of asymmetry should have been a big red flashing


H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.

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