Re: General protection fault in `switch_mm_irqs_off()`

["Lendacky, Thomas" <Thomas.Lendacky@amd.com>]

On 1/10/19 10:49 AM, Paul Menzel wrote:
> Dear Boris, dear Thomas,
> 
> 
> On 01/10/19 17:00, Borislav Petkov wrote:
>> On Thu, Jan 10, 2019 at 02:57:40PM +0100, Paul Menzel wrote:
>>> Thank you very much. Indeed, the machine does not crash. I used Linus’
>>> master branch for testing, and applied your patch on top. Please find
>>> the full log attached.
>>
>>> 80.649: [    3.197107] Spectre V2 : spectre_v2_user_select_mitigation: set X86_FEATURE_USE_IBPB
>>
>> This is amazing.
>>
>> Ok, next diff, same exercise. Thx.> 
>> ---
>> diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
>> index dad12b767ba0..528ef8336f5f 100644
>> --- a/arch/x86/include/asm/nospec-branch.h
>> +++ b/arch/x86/include/asm/nospec-branch.h
>> @@ -284,6 +284,12 @@ static inline void indirect_branch_prediction_barrier(void)
>>  {
>>  	u64 val = PRED_CMD_IBPB;
>>  
>> +	if (WARN_ON(boot_cpu_has(X86_FEATURE_USE_IBPB))) {
>> +		pr_info("%s: c: %px, array: 0x%x\n",
>> +			__func__, &boot_cpu_data, boot_cpu_data.x86_capability[7]);
>> +		return;
>> +	}
>> +
>>  	alternative_msr_write(MSR_IA32_PRED_CMD, val, X86_FEATURE_USE_IBPB);
>>  }
>>  
>> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
>> index 8654b8b0c848..e818e5abe611 100644
>> --- a/arch/x86/kernel/cpu/bugs.c
>> +++ b/arch/x86/kernel/cpu/bugs.c
>> @@ -371,6 +371,9 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
>>  	if (boot_cpu_has(X86_FEATURE_IBPB)) {
>>  		setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
>>  
>> +		pr_err("%s: set X86_FEATURE_USE_IBPB, c: %px, array: 0x%x\n",
>> +			__func__, &boot_cpu_data, boot_cpu_data.x86_capability[7]);
>> +
>>  		switch (cmd) {
>>  		case SPECTRE_V2_USER_CMD_FORCE:
>>  		case SPECTRE_V2_USER_CMD_PRCTL_IBPB:
>> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
>> index cb28e98a0659..8566737fa500 100644
>> --- a/arch/x86/kernel/cpu/common.c
>> +++ b/arch/x86/kernel/cpu/common.c
>> @@ -765,6 +765,9 @@ static void apply_forced_caps(struct cpuinfo_x86 *c)
>>  		c->x86_capability[i] &= ~cpu_caps_cleared[i];
>>  		c->x86_capability[i] |= cpu_caps_set[i];
>>  	}
>> +
>> +	if (c == &boot_cpu_data)
>> +		pr_info("%s: c: %px, array: 0x%x\n", __func__, c, c->x86_capability[7]);
>>  }
>>  
>>  static void init_speculation_control(struct cpuinfo_x86 *c)
>> @@ -778,6 +781,10 @@ static void init_speculation_control(struct cpuinfo_x86 *c)
>>  	if (cpu_has(c, X86_FEATURE_SPEC_CTRL)) {
>>  		set_cpu_cap(c, X86_FEATURE_IBRS);
>>  		set_cpu_cap(c, X86_FEATURE_IBPB);
>> +
>> +		pr_info("%s: X86_FEATURE_SPEC_CTRL: c: %px, array: 0x%x, CPUID: 0x%x\n",
>> +			__func__, c, c->x86_capability[7], cpuid_edx(7));
>> +
>>  		set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);
>>  	}
>>  
>> @@ -793,9 +800,13 @@ static void init_speculation_control(struct cpuinfo_x86 *c)
>>  		set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);
>>  	}
>>  
>> -	if (cpu_has(c, X86_FEATURE_AMD_IBPB))
>> +	if (cpu_has(c, X86_FEATURE_AMD_IBPB)) {
>>  		set_cpu_cap(c, X86_FEATURE_IBPB);
>>  
>> +		pr_info("%s: X86_FEATURE_AMD_IBPB: c: %px, array: 0x%x, CPUID: 0x%x\n",
>> +			__func__, c, c->x86_capability[7], cpuid_ebx(0x80000008));
>> +	}
>> +
>>  	if (cpu_has(c, X86_FEATURE_AMD_STIBP)) {
>>  		set_cpu_cap(c, X86_FEATURE_STIBP);
>>  		set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL);
> 
> Please find the logs attached.

Ah, so the CPUID value is showing X86_FEATURE_AMD_IBPB (not sure why the
cpuid command was showing a value of zero for EBX in your previous email).
Let me see what I can find out about this processor/firmware relation. I
wouldn't expect to see the #GP given that the firmware says IBPB is
supported.

Thanks,
Tom

> 
> 
> Kind regards,
> 
> Paul
>