Hi,
> On 14 Oct 2020, at 22:15, Stefano Stabellini <sstabell...@kernel.org> wrote:
>
> On Wed, 14 Oct 2020, Julien Grall wrote:
>> On 14/10/2020 17:03, Bertrand Marquis wrote:
>>>> On 14 Oct 2020, at 12:35, Andrew Cooper <andrew.coop...@citrix.com> wrote:
>>>>
>>>> On 14/10/2020 11:41, Bertrand Marquis wrote:
>>>>> When a Cortex A57 processor is affected by CPU errata 832075, a guest
>>>>> not implementing the workaround for it could deadlock the system.
>>>>> Add a warning during boot informing the user that only trusted guests
>>>>> should be executed on the system.
>>>>> An equivalent warning is already given to the user by KVM on cores
>>>>> affected by this errata.
>>>>>
>>>>> Signed-off-by: Bertrand Marquis <bertrand.marq...@arm.com>
>>>>> ---
>>>>> xen/arch/arm/cpuerrata.c | 21 +++++++++++++++++++++
>>>>> 1 file changed, 21 insertions(+)
>>>>>
>>>>> diff --git a/xen/arch/arm/cpuerrata.c b/xen/arch/arm/cpuerrata.c
>>>>> index 6c09017515..8f9ab6dde1 100644
>>>>> --- a/xen/arch/arm/cpuerrata.c
>>>>> +++ b/xen/arch/arm/cpuerrata.c
>>>>> @@ -240,6 +240,26 @@ static int enable_ic_inv_hardening(void *data)
>>>>>
>>>>> #endif
>>>>>
>>>>> +#ifdef CONFIG_ARM64_ERRATUM_832075
>>>>> +
>>>>> +static int warn_device_load_acquire_errata(void *data)
>>>>> +{
>>>>> + static bool warned = false;
>>>>> +
>>>>> + if ( !warned )
>>>>> + {
>>>>> + warning_add("This CPU is affected by the errata 832075.\n"
>>>>> + "Guests without required CPU erratum workarounds\n"
>>>>> + "can deadlock the system!\n"
>>>>> + "Only trusted guests should be used on this
>>>>> system.\n");
>>>>> + warned = true;
>>>>
>>>> This is an antipattern, which probably wants fixing elsewhere as well.
>>>>
>>>> warning_add() is __init. It's not legitimate to call from a non-init
>>>> function, and a less useless build system would have modpost to object.
>>>>
>>>> The ARM_SMCCC_ARCH_WORKAROUND_1 instance asserts based on system state,
>>>> but this provides no safety at all.
>>>>
>>>>
>>>> What warning_add() actually does is queue messages for some point near
>>>> the end of boot. It's not clear that this is even a clever thing to do.
>>>>
>>>> I'm very tempted to suggest a blanket change to printk_once().
>>>
>>> If this is needed then this could be done in an other serie ?
>>
>> The callback ->enable() will be called when a CPU is onlined/offlined. So
>> this
>> is going to require if you plan to support CPU hotplugs or suspend resume.
>>
>>> Would be good to keep this patch as purely handling the errata.
>
> My preference would be to keep this patch small with just the errata,
> maybe using a simple printk_once as Andrew and Julien discussed.
>
> There is another instance of warning_add potentially being called
> outside __init in xen/arch/arm/cpuerrata.c:
> enable_smccc_arch_workaround_1. So if you are up for it, it would be
> good to produce a patch to fix that too.
>
>
>> In the case of this patch, how about moving the warning_add() in
>> enable_errata_workarounds()?
>>
>> By then we should now all the errata present on your platform. All CPUs
>> onlined afterwards (i.e. runtime) should always abide to the set discover
>> during boot.
>
> If I understand your suggestion correctly, it would work for
> warn_device_load_acquire_errata, because it is just a warning, but it
> would not work for enable_smccc_arch_workaround_1, because there is
> actually a call to be made there.
>
> Maybe it would be simpler to use printk_once in both cases? I don't have
> a strong preference either way.
I could do the following (in a serie of 2 patches):
- modify enable_smccc_arch_workaround_1 to use printk_once with a
prefix/suffix “****” on each line printed (and maybe adapting print to fit a
line length of 80)
- modify my patch to do the print in enable_errata_workarounds using also
the prefix/suffix and printk_once
Please confirm that this strategy would fit everyone.
Cheers
Bertrand
