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Re: [PATCH V11 10/10] arm/arm64: KVM: add guest SEA support

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  Re: [PATCH V11 10/10] arm/arm64: KVM: add guest SEA support James Morse <james.morse@arm.com> - 2017-03-06 11:40 +0100
    Re: [PATCH V11 10/10] arm/arm64: KVM: add guest SEA support "Baicar, Tyler" <tbaicar@codeaurora.org> - 2017-03-06 15:10 +0100

#1593167 — Re: [PATCH V11 10/10] arm/arm64: KVM: add guest SEA support

Hi Tyler,

On 28/02/17 19:43, Baicar, Tyler wrote:
> On 2/24/2017 3:42 AM, James Morse wrote:
>> On 21/02/17 21:22, Tyler Baicar wrote:
>>> Currently external aborts are unsupported by the guest abort
>>> handling. Add handling for SEAs so that the host kernel reports
>>> SEAs which occur in the guest kernel.

>>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>>> index b2d57fc..403277b 100644
>>> --- a/arch/arm64/mm/fault.c
>>> +++ b/arch/arm64/mm/fault.c
>>> @@ -602,6 +602,24 @@ static const char *fault_name(unsigned int esr)
>>>   }
>>>
>>>   /*
>>> + * Handle Synchronous External Aborts that occur in a guest kernel.
>>> + */
>>> +int handle_guest_sea(unsigned long addr, unsigned int esr)
>>> +{
>>> +    if(IS_ENABLED(HAVE_ACPI_APEI_SEA)) {
>>> +        nmi_enter();
>>> +        ghes_notify_sea();
>>> +        nmi_exit();

>> This nmi stuff was needed for synchronous aborts that may have interrupted
>> APEI's interrupts-masked code. We want to avoid trying to take the same set of
>> locks, hence taking the in_nmi() path through APEI. Here we know we interrupted
>> a guest, so there is no risk that we have interrupted APEI on the host.
>> ghes_notify_sea() can safely take the normal path.

> Makes sense, I can remove the nmi_* calls here.

Just occurs to me: if we do this we need to add the rcu_read_lock() in
ghes_notify_sea() as its not protected by the rcu/nmi weirdness.


Thanks,

James

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#1593368

Hello James,


On 3/6/2017 3:28 AM, James Morse wrote:
> On 28/02/17 19:43, Baicar, Tyler wrote:
>> On 2/24/2017 3:42 AM, James Morse wrote:
>>> On 21/02/17 21:22, Tyler Baicar wrote:
>>>> Currently external aborts are unsupported by the guest abort
>>>> handling. Add handling for SEAs so that the host kernel reports
>>>> SEAs which occur in the guest kernel.
>>>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>>>> index b2d57fc..403277b 100644
>>>> --- a/arch/arm64/mm/fault.c
>>>> +++ b/arch/arm64/mm/fault.c
>>>> @@ -602,6 +602,24 @@ static const char *fault_name(unsigned int esr)
>>>>    }
>>>>
>>>>    /*
>>>> + * Handle Synchronous External Aborts that occur in a guest kernel.
>>>> + */
>>>> +int handle_guest_sea(unsigned long addr, unsigned int esr)
>>>> +{
>>>> +    if(IS_ENABLED(HAVE_ACPI_APEI_SEA)) {
>>>> +        nmi_enter();
>>>> +        ghes_notify_sea();
>>>> +        nmi_exit();
>>> This nmi stuff was needed for synchronous aborts that may have interrupted
>>> APEI's interrupts-masked code. We want to avoid trying to take the same set of
>>> locks, hence taking the in_nmi() path through APEI. Here we know we interrupted
>>> a guest, so there is no risk that we have interrupted APEI on the host.
>>> ghes_notify_sea() can safely take the normal path.
>> Makes sense, I can remove the nmi_* calls here.
> Just occurs to me: if we do this we need to add the rcu_read_lock() in
> ghes_notify_sea() as its not protected by the rcu/nmi weirdness.
>
True, would you suggest leaving these nmi_* calls or adding the rcu_* 
calls? And since that's only needed for this KVM case, shouldn't the 
rcu_* calls just replace the nmi_* calls here (outside of ghes_notify_sea)?

Thanks,
Tyler

-- 
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

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