From: Marc Zyngier <maz@kernel.org>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
kvm@vger.kernel.org, Joey Gouly <joey.gouly@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Zenghui Yu <yuzenghui@huawei.com>,
Bjorn Andersson <andersson@kernel.org>,
Christoffer Dall <christoffer.dall@arm.com>
Subject: Re: [PATCH 06/11] KVM: arm64: nv: Acceletate EL0 counter accesses from hypervisor context
Date: Thu, 05 Dec 2024 11:03:41 +0000 [thread overview]
Message-ID: <86ikrytmr6.wl-maz@kernel.org> (raw)
In-Reply-To: <Z1D1zus18KCpCqjD@linux.dev>
On Thu, 05 Dec 2024 00:37:34 +0000,
Oliver Upton <oliver.upton@linux.dev> wrote:
>
> typo: accelerate
Huh, thanks!
>
> On Mon, Dec 02, 2024 at 05:21:29PM +0000, Marc Zyngier wrote:
[...]
> > + case SYS_CNTVCT_EL0:
> > + case SYS_CNTVCTSS_EL0:
> > + /* If !ELIsInHost(EL2), the guest's CNTVOFF_EL2 applies */
>
> !ELIsInHost(EL0)
No, and that's the whole point. CNTVOFF_EL2 applies at all times when
HCR_EL2==0 and that we're at EL2. From the pseudocode for CNTVCT_EL0:
<quote>
[...]
elsif PSTATE.EL == EL2 then
if !ELIsInHost(EL2) then
X[t, 64] = PhysicalCountInt() - CNTVOFF_EL2;
else
X[t, 64] = PhysicalCountInt();
[...]
</quote>
Which is why we only check E2H, and not E2H+TGE.
It is CNTPOFF_EL2 that applies when !ELIsInHost(EL0), and this is why
it cannot be reliably emulated as we don't (and cannot) track changes
to HCR_EL2.TGE. Yes, this is nonsense.
M.
--
Without deviation from the norm, progress is not possible.
next prev parent reply other threads:[~2024-12-05 11:05 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-12-02 17:21 [PATCH 00/11] KVM: arm64: Add NV timer support Marc Zyngier
2024-12-02 17:21 ` [PATCH 01/11] KVM: arm64: nv: Add handling of EL2-specific timer registers Marc Zyngier
2024-12-02 17:21 ` [PATCH 02/11] KVM: arm64: nv: Sync nested timer state with FEAT_NV2 Marc Zyngier
2024-12-05 0:26 ` Oliver Upton
2024-12-02 17:21 ` [PATCH 03/11] KVM: arm64: nv: Publish emulated timer interrupt state in the in-memory state Marc Zyngier
2024-12-02 17:21 ` [PATCH 04/11] KVM: arm64: nv: Use FEAT_ECV to trap access to EL0 timers Marc Zyngier
2024-12-02 17:21 ` [PATCH 05/11] KVM: arm64: nv: Accelerate EL0 timer read accesses when FEAT_ECV in use Marc Zyngier
2024-12-02 17:21 ` [PATCH 06/11] KVM: arm64: nv: Acceletate EL0 counter accesses from hypervisor context Marc Zyngier
2024-12-05 0:37 ` Oliver Upton
2024-12-05 11:03 ` Marc Zyngier [this message]
2024-12-05 17:07 ` Oliver Upton
2024-12-05 12:07 ` Joey Gouly
2024-12-05 13:31 ` Marc Zyngier
2024-12-02 17:21 ` [PATCH 07/11] KVM: arm64: Handle counter access early in non-HYP context Marc Zyngier
2024-12-02 17:21 ` [PATCH 08/11] KVM: arm64: nv: Add trap routing for CNTHCTL_EL2.EL1{NVPCT,NVVCT,TVT,TVCT} Marc Zyngier
2024-12-02 17:21 ` [PATCH 09/11] KVM: arm64: nv: Propagate CNTHCTL_EL2.EL1NV{P,V}CT bits Marc Zyngier
2024-12-02 17:21 ` [PATCH 10/11] KVM: arm64: nv: Sanitise CNTHCTL_EL2 Marc Zyngier
2024-12-02 17:21 ` [PATCH 11/11] KVM: arm64: Work around x1e's CNTVOFF_EL2 bogosity Marc Zyngier
2024-12-05 0:40 ` [PATCH 00/11] KVM: arm64: Add NV timer support Oliver Upton
2024-12-09 14:24 ` Chase Conklin
2024-12-09 15:15 ` Marc Zyngier
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