linux-kernel - Re: [PATCH 0/7] arm64/boot: Enable EL2 requirements for FEAT

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Message-ID: <7f5c68c7-8036-4d18-950f-80e55ac8ea11@arm.com>
Date: Tue, 28 Jan 2025 14:41:17 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Rob Herring <robh@...nel.org>, Catalin Marinas <catalin.marinas@....com>
Cc: Marc Zyngier <maz@...nel.org>, linux-arm-kernel@...ts.infradead.org,
 Will Deacon <will@...nel.org>, Ryan Roberts <ryan.roberts@....com>,
 Mark Rutland <mark.rutland@....com>, Oliver Upton <oliver.upton@...ux.dev>,
 Jonathan Corbet <corbet@....net>, Eric Auger <eric.auger@...hat.com>,
 kvmarm@...ts.linux.dev, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/7] arm64/boot: Enable EL2 requirements for FEAT_PMUv3p9



On 1/18/25 03:37, Rob Herring wrote:
> On Thu, Jan 16, 2025 at 9:32 AM Catalin Marinas <catalin.marinas@....com> wrote:
>>
>> On Wed, Jan 08, 2025 at 07:47:16AM -0600, Rob Herring wrote:
>>> On Wed, Jan 8, 2025 at 5:15 AM Marc Zyngier <maz@...nel.org> wrote:
>>>> On Tue, 07 Jan 2025 22:13:47 +0000,
>>>> Rob Herring <robh@...nel.org> wrote:
>>>>> On Tue, Jan 7, 2025 at 6:13 AM Catalin Marinas <catalin.marinas@....com> wrote:
>>>>>> But does KVM actually expose the feature to EL1 in ID_AA64DFR1_EL1 and
>>>>>> than traps it at EL2?
>>>>>
>>>>> As Marc pointed out KVM only advertises PMUv3.8. Regardless, guest
>>>>> accesses to these registers are trapped with or without this series.
>>>>
>>>> And most probably generates a nice splat in the kernel log, as nobody
>>>> updated KVM to handle *correctly* PMICNTR_EL0 traps, let alone deal
>>>> with the FGT2 registers.
>>>
>>> Isn't that this series[1]? Should that have come first, I guess I know
>>> that *now*.
>> [...]
>>> [1] https://lore.kernel.org/all/20241210055311.780688-1-anshuman.khandual@arm.com/
>>
>> It's not any clearer to me. Does this series depend on the 46-patch one?
>> Or, if we had the other, is this no longer needed? Or none of these,
>> they are independent.
> 
> They are independent. I think ideally we'd want everything landing at
> the same time, but we're past ideal at this point. Without this
> series, if someone uses PMU on v8.9 and firmware enabled FGT2, then
> the kernel will crash. Without the above series, KVM will have
> warnings in the kernel log, but otherwise function.

Right, they are independent. Just that Rob had observed this PMU v3.8 boot
requirement while reviewing the HW breakpoint series earlier. I should just
respin this series after the upcoming v6.14-rc1 release is out ?