Re: [PATCH] x86, microcode: Don't initialize microcode code on paravirt

Re: [PATCH] x86, microcode: Don't initialize microcode code on paravirt

[Konrad Rzeszutek Wilk]

On Mon, Dec 01, 2014 at 04:27:44PM -0500, Boris Ostrovsky wrote:
> Paravirtual guests are not expected to load microcode into processors
> and therefore it is not necessary to initialize microcode loading
> logic.

CC-ing the KVM folks since they use the paravirt interface too.
> 
> In fact, under certain circumstances initializing this logic may cause
> the guest to crash. Specifically, 32-bit kernels use __pa_nodebug()
> macro which does not work in Xen (the code path that leads to this macro
> happens during resume when we call mc_bp_resume()->load_ucode_ap()
> ->check_loader_disabled_ap())
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> ---
>  arch/x86/kernel/cpu/microcode/core.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
> index 2ce9051..ebd232d 100644
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/arch/x86/kernel/cpu/microcode/core.c
> @@ -557,7 +557,7 @@ static int __init microcode_init(void)
>  	struct cpuinfo_x86 *c = &cpu_data(0);
>  	int error;
>  
> -	if (dis_ucode_ldr)
> +	if (paravirt_enabled() || dis_ucode_ldr)
>  		return 0;
>  
>  	if (c->x86_vendor == X86_VENDOR_INTEL)
> -- 
> 1.7.1
> 

Re: [PATCH] x86, microcode: Don't initialize microcode code on paravirt

[Paolo Bonzini]

On 01/12/2014 22:57, Konrad Rzeszutek Wilk wrote:
> On Mon, Dec 01, 2014 at 04:27:44PM -0500, Boris Ostrovsky wrote:
>> Paravirtual guests are not expected to load microcode into processors
>> and therefore it is not necessary to initialize microcode loading
>> logic.
> 
> CC-ing the KVM folks since they use the paravirt interface too.

We also do not want to load microcode. :)  Thanks for the heads-up.

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo

>> In fact, under certain circumstances initializing this logic may cause
>> the guest to crash. Specifically, 32-bit kernels use __pa_nodebug()
>> macro which does not work in Xen (the code path that leads to this macro
>> happens during resume when we call mc_bp_resume()->load_ucode_ap()
>> ->check_loader_disabled_ap())
>>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>> ---
>>  arch/x86/kernel/cpu/microcode/core.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
>> index 2ce9051..ebd232d 100644
>> --- a/arch/x86/kernel/cpu/microcode/core.c
>> +++ b/arch/x86/kernel/cpu/microcode/core.c
>> @@ -557,7 +557,7 @@ static int __init microcode_init(void)
>>  	struct cpuinfo_x86 *c = &cpu_data(0);
>>  	int error;
>>  
>> -	if (dis_ucode_ldr)
>> +	if (paravirt_enabled() || dis_ucode_ldr)
>>  		return 0;
>>  
>>  	if (c->x86_vendor == X86_VENDOR_INTEL)
>> -- 
>> 1.7.1
>>

Re: [PATCH] x86, microcode: Don't initialize microcode code on paravirt

[Borislav Petkov]

On Mon, Dec 01, 2014 at 11:12:38PM +0100, Paolo Bonzini wrote:
> We also do not want to load microcode. :)  Thanks for the heads-up.

You don't need to :P

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--

Re: [PATCH] x86, microcode: Don't initialize microcode code on paravirt

[Boris Ostrovsky]

On 12/01/2014 05:00 PM, Borislav Petkov wrote:
> On Mon, Dec 01, 2014 at 04:27:44PM -0500, Boris Ostrovsky wrote:
>> Paravirtual guests are not expected to load microcode into processors
>> and therefore it is not necessary to initialize microcode loading
>> logic.
>>
>> In fact, under certain circumstances initializing this logic may cause
>> the guest to crash. Specifically, 32-bit kernels use __pa_nodebug()
>> macro which does not work in Xen (the code path that leads to this macro
>> happens during resume when we call mc_bp_resume()->load_ucode_ap()
>> ->check_loader_disabled_ap())
>>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>> ---
>>   arch/x86/kernel/cpu/microcode/core.c |    2 +-
>>   1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
>> index 2ce9051..ebd232d 100644
>> --- a/arch/x86/kernel/cpu/microcode/core.c
>> +++ b/arch/x86/kernel/cpu/microcode/core.c
>> @@ -557,7 +557,7 @@ static int __init microcode_init(void)
>>   	struct cpuinfo_x86 *c = &cpu_data(0);
>>   	int error;
>>   
>> -	if (dis_ucode_ldr)
>> +	if (paravirt_enabled() || dis_ucode_ldr)
> Ok, let me make sure I understand this correctly: The early path doesn't
> get executed on paravirt, i.e. the path along load_ucode_intel_ap()?

(+KVM folks here as well)

Xen PV doesn't start with startup_32()/startup_32_smp() so for Xen this 
is true. Don't know about KVM (or lguest).

>
> And you want to avoid loading of the microcode driver because the only
> path we come to load_ucode_ap() on paravirt is the hotplug notifier?

That's my understanding, yes.

>
> Btw, we've applied another fix today for 3.18 final which limits the
> microcode reloading to 64-bit only:
>
> http://git.kernel.org/tip/02ecc41abcea4ff9291d548f6f846b29b354ddd2
>
> which should accidentally fix the paravirt issue too, no?

I think so. The problem we have now is __pa() macro that we only use on 
32-bit. I'll queue this for overnight tests to make sure and if it 
indeed works then 3.19 should be fine.

Thanks.
-boris

>
> Because if so, I'd like to delay your patch for the 3.19 merge window
> unless absolutely necessary.
>
> Thanks.
>

Re: [PATCH] x86, microcode: Don't initialize microcode code on paravirt

[Borislav Petkov]

On Mon, Dec 01, 2014 at 05:31:56PM -0500, Boris Ostrovsky wrote:
> I think so. The problem we have now is __pa() macro that we only use
> on 32-bit. I'll queue this for overnight tests to make sure and if it
> indeed works then 3.19 should be fine.

Cool, thanks.

I'd still take your patch for 3.19 though because I'm fixing the 32-bit
reloading path properly and will remove the ifdef afterwards.

And even then, I'd like to prevent loading the module on a paravirt
guest if it is totally unneeded there.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--

Re: [PATCH] x86, microcode: Don't initialize microcode code on paravirt

[Boris Ostrovsky]

On 12/01/2014 05:37 PM, Borislav Petkov wrote:
> On Mon, Dec 01, 2014 at 05:31:56PM -0500, Boris Ostrovsky wrote:
>> I think so. The problem we have now is __pa() macro that we only use
>> on 32-bit. I'll queue this for overnight tests to make sure and if it
>> indeed works then 3.19 should be fine.
> Cool, thanks.

All tests passed.

> I'd still take your patch for 3.19 though because I'm fixing the 32-bit
> reloading path properly and will remove the ifdef afterwards.
>
> And even then, I'd like to prevent loading the module on a paravirt
> guest if it is totally unneeded there.
>

I wonder whether we should prevent all guests (not just paravirt) from 
loading microcode driver (and from doing early microcode loading).

-boris

Re: [PATCH] x86, microcode: Don't initialize microcode code on paravirt

[Borislav Petkov]

On Tue, Dec 02, 2014 at 09:36:40AM -0500, Boris Ostrovsky wrote:
> All tests passed.

Thanks!

> I wonder whether we should prevent all guests (not just paravirt) from
> loading microcode driver (and from doing early microcode loading).

I don't think the unmodified ones need to. At least I haven't seen any
issues so far.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.