From: Marc Zyngier <maz@kernel.org>
To: James Morse <james.morse@arm.com>
Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH 3/5] kvm: arm64: Limit PMU version to ARMv8.1
Date: Wed, 19 Feb 2020 11:14:40 +0000 [thread overview]
Message-ID: <89155997285a33615093210d6c4de26d@kernel.org> (raw)
In-Reply-To: <ed7f31d5-9a2b-6ea0-85f8-74fcd7d9ac61@arm.com>
On 2020-02-19 10:18, James Morse wrote:
> Hi Marc,
>
> On 2/19/20 9:46 AM, Marc Zyngier wrote:
>> On 2020-02-18 17:43, James Morse wrote:
>>> Hi Marc,
>>>
>>> On 16/02/2020 18:53, Marc Zyngier wrote:
>>>> Our PMU code is only implementing the ARMv8.1 features, so let's
>>>> stick to this when reporting the feature set to the guest.
>>>
>>>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>>>> index 682fedd7700f..06b2d0dc6c73 100644
>>>> --- a/arch/arm64/kvm/sys_regs.c
>>>> +++ b/arch/arm64/kvm/sys_regs.c
>>>> @@ -1093,6 +1093,11 @@ static u64 read_id_reg(const struct kvm_vcpu
>>>> *vcpu,
>>>> FEATURE(ID_AA64ISAR1_GPA) |
>>>> FEATURE(ID_AA64ISAR1_GPI));
>>>> break;
>>>> + case SYS_ID_AA64DFR0_EL1:
>>>> + /* Limit PMU to ARMv8.1 */
>>>
>>> Not just limit, but upgrade too! (force?)
>>> This looks safe because ARMV8_PMU_EVTYPE_EVENT always includes the
>>> extra bits this added, and the register is always trapped.
>>
>> That's definitely not what I intended! Let me fix that one.
>
> What goes wrong?
>
> The register description says to support v8.1 you need:
> | Extended 16-bit PMEVTYPER<n>_EL0.evtCount field
> | If EL2 is implemented, the MDCR_EL2.HPMD control bit
>
> It looks like the extended PMEVTYPER would work via the emulation, and
> EL2 guests are totally crazy.
>
> Is the STALL_* bits in ARMv8.1-PMU the problem, ... or the extra work
> for NV?
What goes wrong is that on a v8.0 system, the guest could be tempted to
use events in the 0x0400-0xffff range. It wouldn't break anything, but
it wouldn't give the expected result.
I don't care much for PMU support in EL2 guests at this stage.
>>> The PMU version is also readable via ID_DFR0_EL1.PerfMon, should that
>>> be sanitised to be the same? (I don't think we've hidden an aarch64
>>> feature that also existed in aarch32 before).
>>
>> Indeed, yet another oversight. I'll fix that too.
>
> (Weird variation in the aarch32 and aarch64 ID registers isn't
> something
> I care about ... who would ever look at both?)
A 64bit guest running a 32bit EL0?
M.
--
Jazz is not dead. It just smells funny...
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next prev parent reply other threads:[~2020-02-19 11:14 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-16 18:53 [PATCH 0/5] Random debug/PMU fixes for 5.6 Marc Zyngier
2020-02-16 18:53 ` [PATCH 1/5] KVM: arm64: Fix missing RES1 in emulation of DBGBIDR Marc Zyngier
2020-02-18 17:43 ` James Morse
2020-02-18 18:01 ` Robin Murphy
2020-02-18 18:15 ` James Morse
2020-02-16 18:53 ` [PATCH 2/5] KVM: arm64: Refactor filtering of ID registers Marc Zyngier
2020-02-20 14:12 ` Andre Przywara
2020-02-16 18:53 ` [PATCH 3/5] kvm: arm64: Limit PMU version to ARMv8.1 Marc Zyngier
2020-02-18 17:43 ` James Morse
2020-02-19 9:46 ` Marc Zyngier
2020-02-19 10:18 ` James Morse
2020-02-19 11:14 ` Marc Zyngier [this message]
2020-02-16 18:53 ` [PATCH 4/5] KVM: arm64: Limit the debug architecture to ARMv8.0 Marc Zyngier
2020-02-18 17:45 ` James Morse
2020-02-16 18:53 ` [PATCH 5/5] KVM: arm64: Upgrade PMU support to ARMv8.4 Marc Zyngier
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