Re: General protection fault in `switch_mm_irqs_off()`

Paul Menzel
2019-01-14T17:09:43Z

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Dear Thomas,

Thank you for checking this, and coming back with the results so quickly.

On 01/14/19 18:00, Lendacky, Thomas wrote:
> On 1/10/19 12:34 PM, Lendacky, Thomas wrote:
>> 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.
>
> I'm not able to reproduce this issue on my family 21, model 1, stepping 2
> processor (AMD Opteron(TM) Processor 6274) as I am able to successfully
> write to the PRED_CMD MSR.

It’s not exactly the same processor, but I guess the same family should be
good enough. What board do you have? Do you have two sockets, and both
populated?

Here is an Asus KGPE-D16 with two AMD Opterons put in.

Lastly, my microcode updates are applied in firmware, and not by GNU/Linux.

> Let's check the firmware file that you're loading. The one I'm using is:
>
> $ sha1sum /lib/firmware/amd-ucode/microcode_amd_fam15h.bin
> 90896256951d8edf7baf8181ae11e2dc618a5171 /lib/firmware/amd-ucode/microcode_amd_fam15h.bin
>
> Does that match what you have?

Yes, that matches exactly.

90896256951d8edf7baf8181ae11e2dc618a5171 3rdparty/blobs/cpu/amd/family_15h/microcode_amd_fam15h.bin

Kind regards,

Paul

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