From: Christophe de Dinechin <christophe.de.dinechin@gmail.com>
To: Steven Price <steven.price@arm.com>
Cc: kvm@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
linux-doc@vger.kernel.org, Russell King <linux@armlinux.org.uk>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Marc Zyngier <maz@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Will Deacon <will@kernel.org>,
kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH 1/9] KVM: arm64: Document PV-time interface
Date: Mon, 05 Aug 2019 18:40:54 +0200 [thread overview]
Message-ID: <m1mugnmv0x.fsf@dinechin.org> (raw)
In-Reply-To: <20190802145017.42543-2-steven.price@arm.com>
Steven Price writes:
> Introduce a paravirtualization interface for KVM/arm64 based on the
> "Arm Paravirtualized Time for Arm-Base Systems" specification DEN 0057A.
>
> This only adds the details about "Stolen Time" as the details of "Live
> Physical Time" have not been fully agreed.
>
[...]
> +
> +Stolen Time
> +-----------
> +
> +The structure pointed to by the PV_TIME_ST hypercall is as follows:
> +
> + Field | Byte Length | Byte Offset | Description
> + ----------- | ----------- | ----------- | --------------------------
> + Revision | 4 | 0 | Must be 0 for version 0.1
> + Attributes | 4 | 4 | Must be 0
> + Stolen time | 8 | 8 | Stolen time in unsigned
> + | | | nanoseconds indicating how
> + | | | much time this VCPU thread
> + | | | was involuntarily not
> + | | | running on a physical CPU.
I know very little about the topic, but I don't understand how the spec
as proposed allows an accurate reading of the relation between physical
time and stolen time simultaneously. In other words, could you draw
Figure 1 of the spec from within the guest? Or is it a non-objective?
For example, if you read the stolen time before you read CNTVCT_EL0,
isn't it possible for a lengthy event like a migration to occur between
the two reads, causing the stolen time to be obsolete and off by seconds?
--
Cheers,
Christophe de Dinechin (IRC c3d)
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
next prev parent reply other threads:[~2019-08-06 9:39 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-02 14:50 [PATCH 0/9] arm64: Stolen time support Steven Price
2019-08-02 14:50 ` [PATCH 1/9] KVM: arm64: Document PV-time interface Steven Price
2019-08-03 11:13 ` Marc Zyngier
2019-08-05 13:06 ` Steven Price
2019-08-05 3:23 ` Zenghui Yu
2019-08-05 13:06 ` Steven Price
2019-08-05 16:40 ` Christophe de Dinechin [this message]
2019-08-07 13:21 ` Steven Price
2019-08-07 14:28 ` Christophe de Dinechin
2019-08-07 15:26 ` Steven Price
2019-08-02 14:50 ` [PATCH 2/9] KVM: arm/arm64: Factor out hypercall handling from PSCI code Steven Price
2019-08-02 14:50 ` [PATCH 3/9] KVM: arm64: Implement PV_FEATURES call Steven Price
2019-08-03 11:21 ` Marc Zyngier
2019-08-05 13:14 ` Steven Price
2019-08-02 14:50 ` [PATCH 4/9] KVM: arm64: Support stolen time reporting via shared structure Steven Price
2019-08-03 11:55 ` Marc Zyngier
2019-08-05 14:09 ` Steven Price
2019-08-03 17:58 ` Marc Zyngier
2019-08-03 18:13 ` Marc Zyngier
2019-08-05 14:18 ` Steven Price
2019-08-02 14:50 ` [PATCH 5/9] KVM: Allow kvm_device_ops to be const Steven Price
2019-08-02 14:50 ` [PATCH 6/9] KVM: arm64: Provide a PV_TIME device to user space Steven Price
2019-08-03 12:51 ` Marc Zyngier
2019-08-03 17:34 ` Marc Zyngier
2019-08-07 13:39 ` Steven Price
2019-08-07 13:51 ` Marc Zyngier
2019-08-05 16:10 ` Steven Price
2019-08-05 16:28 ` Marc Zyngier
2019-08-02 14:50 ` [PATCH 7/9] arm/arm64: Provide a wrapper for SMCCC 1.1 calls Steven Price
2019-08-05 10:03 ` Will Deacon
2019-08-02 14:50 ` [PATCH 8/9] arm/arm64: Make use of the SMCCC 1.1 wrapper Steven Price
2019-08-02 14:50 ` [PATCH 9/9] arm64: Retrieve stolen time as paravirtualized guest Steven Price
2019-08-04 9:53 ` Marc Zyngier
2019-08-08 15:29 ` Steven Price
2019-08-08 15:49 ` Marc Zyngier
2019-08-09 13:51 ` Zenghui Yu
2019-08-12 10:39 ` Steven Price
2019-08-13 6:06 ` Zenghui Yu
2019-08-03 18:05 ` [PATCH 0/9] arm64: Stolen time support Marc Zyngier
2019-08-05 13:06 ` Steven Price
2019-08-05 13:26 ` Marc Zyngier
2019-08-14 13:02 ` Alexander Graf
2019-08-14 14:19 ` Marc Zyngier
2019-08-14 14:52 ` [UNVERIFIED SENDER] " Alexander Graf
2019-08-16 10:23 ` Steven Price
2020-07-21 3:26 ` zhukeqian
2020-07-27 10:48 ` Steven Price
2020-07-29 2:57 ` zhukeqian
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=m1mugnmv0x.fsf@dinechin.org \
--to=christophe.de.dinechin@gmail.com \
--cc=catalin.marinas@arm.com \
--cc=kvm@vger.kernel.org \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@armlinux.org.uk \
--cc=maz@kernel.org \
--cc=pbonzini@redhat.com \
--cc=steven.price@arm.com \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).