From: Marc Zyngier <maz@kernel.org>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: kvmarm@lists.linux.dev, kvm@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Zenghui Yu <yuzenghui@huawei.com>,
Ricardo Koller <ricarkol@google.com>,
Simon Veith <sveith@amazon.de>,
dwmw2@infradead.org
Subject: Re: [PATCH 08/16] KVM: arm64: timers: Allow userspace to set the counter offsets
Date: Thu, 09 Mar 2023 08:25:09 +0000 [thread overview]
Message-ID: <87edpy9vru.wl-maz@kernel.org> (raw)
In-Reply-To: <ZAg9ONoYhUoa0mH9@linux.dev>
Hi Oliver,
On Wed, 08 Mar 2023 07:46:00 +0000,
Oliver Upton <oliver.upton@linux.dev> wrote:
[...]
> I certainly agree that (2a) is highly desirable to get existing VMMs to
> 'do the right thing' for free. Playing devil's advocate, would this not
> also break the tracing example you've given of correlating timestamps
> between the host and guest? I wouldn't expect a userspace + VM tracing
> contraption to live migrate but restoring from a snapshot seems
> plausible.
It really depends when this VM was saved.
If you saved it on an old host that doesn't expose CNTPCT and restore
it on a new host, the physical offset is still zero (this is already
special-cased), and there is no difference in behaviour.
If you saved it from a host that does expose CNTPCT, then the
behaviour changes. But should we really care?
> Regardless, I like the general direction you've proposed. IIUC, you'll
> want to go ahead with ignoring writes to CNT{P,V}CT if the offset was
> written by userspace, right?
That'd be my preference in order not to break the "blind restore"
behaviour that QEMU already uses for about everything.
I'll repost the series shortly, as it has grown some extra goodies
such as moving the PPI settings out of the way...
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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next prev parent reply other threads:[~2023-03-09 8:26 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-16 14:21 [PATCH 00/16] KVM: arm64: Rework timer offsetting for fun and profit Marc Zyngier
2023-02-16 14:21 ` [PATCH 01/16] arm64: Add CNTPOFF_EL2 register definition Marc Zyngier
2023-02-16 14:21 ` [PATCH 02/16] arm64: Add HAS_ECV_CNTPOFF capability Marc Zyngier
2023-02-22 4:30 ` Reiji Watanabe
2023-02-22 10:47 ` Marc Zyngier
2023-02-16 14:21 ` [PATCH 03/16] kvm: arm64: Expose {un,}lock_all_vcpus() to the reset of KVM Marc Zyngier
2023-02-23 22:30 ` Colton Lewis
2023-02-16 14:21 ` [PATCH 04/16] KVM: arm64: timers: Use a per-vcpu, per-timer accumulator for fractional ns Marc Zyngier
2023-02-23 22:30 ` Colton Lewis
2023-02-16 14:21 ` [PATCH 05/16] KVM: arm64: timers: Convert per-vcpu virtual offset to a global value Marc Zyngier
2023-02-22 6:15 ` Reiji Watanabe
2023-02-22 10:54 ` Marc Zyngier
2023-02-16 14:21 ` [PATCH 06/16] KVM: arm64: timers: Use CNTPOFF_EL2 to offset the physical timer Marc Zyngier
2023-02-23 22:34 ` Colton Lewis
2023-02-24 8:59 ` Marc Zyngier
2023-02-16 14:21 ` [PATCH 07/16] KVM: arm64: timers: Allow physical offset without CNTPOFF_EL2 Marc Zyngier
2023-02-23 22:40 ` Colton Lewis
2023-02-24 10:54 ` Marc Zyngier
2023-02-16 14:21 ` [PATCH 08/16] KVM: arm64: timers: Allow userspace to set the counter offsets Marc Zyngier
2023-02-16 22:09 ` Oliver Upton
2023-02-17 10:17 ` Marc Zyngier
2023-02-17 22:11 ` Oliver Upton
2023-02-22 11:56 ` Marc Zyngier
2023-02-22 16:34 ` Oliver Upton
2023-02-23 18:25 ` Marc Zyngier
2023-03-08 7:46 ` Oliver Upton
2023-03-08 7:53 ` Oliver Upton
2023-03-09 8:29 ` Marc Zyngier
2023-03-09 8:25 ` Marc Zyngier [this message]
2023-02-23 22:41 ` Colton Lewis
2023-02-24 11:24 ` Marc Zyngier
2023-02-16 14:21 ` [PATCH 09/16] KVM: arm64: timers: Allow save/restoring of the physical timer Marc Zyngier
2023-02-16 14:21 ` [PATCH 10/16] KVM: arm64: timers: Rationalise per-vcpu timer init Marc Zyngier
2023-02-16 14:21 ` [PATCH 11/16] KVM: arm64: Document KVM_ARM_SET_CNT_OFFSETS and co Marc Zyngier
2023-02-16 14:21 ` [PATCH 12/16] KVM: arm64: nv: timers: Add a per-timer, per-vcpu offset Marc Zyngier
2023-02-24 20:07 ` Colton Lewis
2023-02-25 10:32 ` Marc Zyngier
2023-02-16 14:21 ` [PATCH 13/16] KVM: arm64: nv: timers: Support hyp timer emulation Marc Zyngier
2023-02-24 20:08 ` Colton Lewis
2023-02-25 10:34 ` Marc Zyngier
2023-02-16 14:21 ` [PATCH 14/16] KVM: arm64: selftests: Add physical timer registers to the sysreg list Marc Zyngier
2023-02-16 14:21 ` [PATCH 15/16] KVM: arm64: selftests: Augment existing timer test to handle variable offsets Marc Zyngier
2023-03-06 22:08 ` Colton Lewis
2023-03-09 9:01 ` Marc Zyngier
2023-03-10 19:26 ` Colton Lewis
2023-03-12 15:53 ` Marc Zyngier
2023-03-13 11:43 ` Marc Zyngier
2023-03-14 17:47 ` Colton Lewis
2023-03-14 18:18 ` Marc Zyngier
2023-02-16 14:21 ` [PATCH 16/16] KVM: arm64: selftests: Deal with spurious timer interrupts Marc Zyngier
2023-02-21 16:28 ` [PATCH 00/16] KVM: arm64: Rework timer offsetting for fun and profit Veith, Simon
2023-02-21 22:17 ` Marc Zyngier
2023-02-23 22:29 ` Colton Lewis
2023-02-24 8:45 ` Marc Zyngier
2023-02-24 20:07 ` Colton Lewis
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