[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <6935be08-f29e-4dd1-9fe7-3d51d3f97509@redhat.com>
Date: Wed, 26 Jun 2024 15:33:43 +0800
From: Shaoqin Huang <shahuang@...hat.com>
To: Marc Zyngier <maz@...nel.org>
Cc: Oliver Upton <oliver.upton@...ux.dev>, kvmarm@...ts.linux.dev,
James Morse <james.morse@....com>, Suzuki K Poulose
<suzuki.poulose@....com>, Zenghui Yu <yuzenghui@...wei.com>,
Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] KVM: arm64: Allow userspace to change
ID_AA64PFR1_EL1
Hi Marc,
On 6/21/24 15:53, Marc Zyngier wrote:
> On Fri, 21 Jun 2024 07:17:57 +0100,
> Shaoqin Huang <shahuang@...hat.com> wrote:
>>
>> Hi Marc,
>>
>> On 6/18/24 15:39, Marc Zyngier wrote:
>>> On Tue, 18 Jun 2024 07:38:06 +0100,
>>> Shaoqin Huang <shahuang@...hat.com> wrote:
>>>>
>>>> Allow userspace to change the guest-visible value of the register with
>>>> some severe limitation:
>>>>
>>>> - No changes to features not virtualized by KVM (MPAM_frac, RAS_frac)
>>>> ---
>>>> arch/arm64/kvm/sys_regs.c | 3 ++-
>>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>>>> index 22b45a15d068..bead81867bce 100644
>>>> --- a/arch/arm64/kvm/sys_regs.c
>>>> +++ b/arch/arm64/kvm/sys_regs.c
>>>> @@ -2306,7 +2306,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>>>> ID_AA64PFR0_EL1_GIC |
>>>> ID_AA64PFR0_EL1_AdvSIMD |
>>>> ID_AA64PFR0_EL1_FP), },
>>>> - ID_SANITISED(ID_AA64PFR1_EL1),
>>>> + ID_WRITABLE(ID_AA64PFR1_EL1, ~(ID_AA64PFR1_EL1_RAS_frac |
>>>> + ID_AA64PFR1_EL1_MPAM_frac)),
>>>> ID_UNALLOCATED(4,2),
>>>> ID_UNALLOCATED(4,3),
>>>> ID_WRITABLE(ID_AA64ZFR0_EL1, ~ID_AA64ZFR0_EL1_RES0),
>>>
>>> This isn't a valid patch.
>>>
>>> Furthermore, how about all the other features that may or may not be
>>> currently handled by KVM? Please see [1] and make sure that all
>>> existing fields have a known behaviour (a combination of masked,
>>> preserved, capped, writable or read-only).
>>>
>>> I can at least see problems with MTE_frac and MTEX, plus all the other
>>> things that KVM doesn't know how to save/restore (THE, GCS, NMI...).
>>>
>>> What I asked you to handle the whole register, I really meant it.
>>
>> I currently only found the BT and SSBS fields can be written without
>> any unknown behavior.
>
> I can only assume you haven't looked hard enough.
>
>>
>> All other fields in the ID_AA64PFR1_EL1 are either not supported by
>> KVM or the field involved with other register and KVM don't know how
>> to handle them.
>
> Why can't CSV2_frac be writable? Why can't most of the other fields be
> hidden depending on the VM configuration, as pointed out above?
I looked at the "struct arm64_ftr_bits ftr_id_aa64pfr1[]" in the
kernel/cpufeature.c, I don't see the CSV2_frac has been supported on ARM
bare-mental. In this situation, can we first support it in KVM? If so,
how can we do that, I don't understand that, could you give me some
hints about that.
Other fields are same with CSV2_frac I think. The KVM don't know the
configuration about them. Why we should allow them writable and hidden
them right now? Instead of just make them still unwrittable?
Thanks,
Shaoqin
>
> M.
>
--
Shaoqin
Powered by blists - more mailing lists