From: Thomas Gleixner <tglx@linutronix.de>
To: Hikaru Nishida <hikalium@chromium.org>,
linux-kernel@vger.kernel.org, dme@dme.org, mlevitsk@redhat.com
Cc: suleiman@google.com, Hikaru Nishida <hikalium@chromium.org>,
Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
Ingo Molnar <mingo@redhat.com>, Jim Mattson <jmattson@google.com>,
Joerg Roedel <joro@8bytes.org>,
John Stultz <john.stultz@linaro.org>,
Juergen Gross <jgross@suse.com>,
Lai Jiangshan <laijs@linux.alibaba.com>,
Mike Travis <mike.travis@hpe.com>,
Paolo Bonzini <pbonzini@redhat.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Sean Christopherson <seanjc@google.com>,
Stephen Boyd <sboyd@kernel.org>,
Tom Lendacky <thomas.lendacky@amd.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
kvm@vger.kernel.org, x86@kernel.org
Subject: Re: [v2 PATCH 4/4] x86/kvm: Add guest side support for virtual suspend time injection
Date: Tue, 10 Aug 2021 17:48:02 +0200 [thread overview]
Message-ID: <87lf59qp1p.ffs@tglx> (raw)
In-Reply-To: <20210806190607.v2.4.I2cbcd43256eacc3c92274adff6d0458b6a9c15ee@changeid>
On Fri, Aug 06 2021 at 19:07, Hikaru Nishida wrote:
> arch/x86/Kconfig | 13 ++++++++++
> arch/x86/include/asm/idtentry.h | 4 +++
> arch/x86/include/asm/kvm_para.h | 9 +++++++
> arch/x86/kernel/kvmclock.c | 40 +++++++++++++++++++++++++++++
> include/linux/timekeeper_internal.h | 4 +++
> kernel/time/timekeeping.c | 33 ++++++++++++++++++++++++
Again, this wants to be split into infrastructure and usage.
> --- a/include/linux/timekeeper_internal.h
> +++ b/include/linux/timekeeper_internal.h
> @@ -124,6 +124,10 @@ struct timekeeper {
> u32 ntp_err_mult;
> /* Flag used to avoid updating NTP twice with same second */
> u32 skip_second_overflow;
> +#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING_GUEST
> + /* suspend_time_injected keeps the duration injected through kvm */
> + u64 suspend_time_injected;
This is KVM only, so please can we have a name for that struct member
which reflects this?
> +#endif
> #ifdef CONFIG_DEBUG_TIMEKEEPING
> long last_warning;
> /*
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index 3ac3fb479981..424c61d38646 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -2125,6 +2125,39 @@ static u64 logarithmic_accumulation(struct timekeeper *tk, u64 offset,
> return offset;
> }
>
> +#ifdef CONFIG_KVM_VIRT_SUSPEND_TIMING_GUEST
> +/*
> + * timekeeping_inject_virtual_suspend_time - Inject virtual suspend time
> + * when requested by the kvm host.
If this is an attempt to provide a kernel-doc comment for this function,
then it's clearly a failed attempt and aside of that malformatted.
> + * This function should be called under irq context.
Why? There is no reason for being called from interrupt context and
nothing inforces it.
> + */
> +void timekeeping_inject_virtual_suspend_time(void)
> +{
> + /*
> + * Only updates shadow_timekeeper so the change will be reflected
> + * on the next call of timekeeping_advance().
No. That's broken.
timekeeping_inject_virtual_suspend_time();
do_settimeofday() or do_adjtimex()
timekeeping_update(tk, TK_MIRROR...);
and your change to the shadow timekeeper is gone.
Of course there is also no justification for this approach. What's wrong
with updating it right away?
> + */
> + struct timekeeper *tk = &shadow_timekeeper;
> + unsigned long flags;
> + struct timespec64 delta;
> + u64 suspend_time;
Please sort variables in reverse fir tree order and not randomly as you
see fit.
> +
> + raw_spin_lock_irqsave(&timekeeper_lock, flags);
> + suspend_time = kvm_get_suspend_time();
> + if (suspend_time > tk->suspend_time_injected) {
> + /*
> + * Do injection only if the time is not injected yet.
> + * suspend_time and tk->suspend_time_injected values are
> + * cummrative, so take a diff and inject the duration.
cummrative?
> + */
> + delta = ns_to_timespec64(suspend_time - tk->suspend_time_injected);
> + __timekeeping_inject_sleeptime(tk, &delta);
> + tk->suspend_time_injected = suspend_time;
It's absolutely unclear how this storage and diff magic works and the
comment is not helping someone not familiar with the implementation of
kvm_get_suspend_time() and the related code at all. Please explain
non-obvious logic properly.
Thanks,
tglx
prev parent reply other threads:[~2021-08-10 15:48 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-06 10:07 [v2 PATCH 0/4] x86/kvm: Virtual suspend time injection support Hikaru Nishida
2021-08-06 10:07 ` [v2 PATCH 1/4] x86/kvm: Reserve KVM_FEATURE_HOST_SUSPEND_TIME and MSR_KVM_HOST_SUSPEND_TIME Hikaru Nishida
2021-08-06 10:07 ` [v2 PATCH 2/4] x86/kvm: Add definitions for virtual suspend time injection Hikaru Nishida
2021-08-10 15:14 ` Thomas Gleixner
2021-08-13 18:36 ` Guenter Roeck
2021-08-06 10:07 ` [v2 PATCH 3/4] x86/kvm: Add host side support " Hikaru Nishida
2021-08-10 15:21 ` Thomas Gleixner
2021-08-10 15:24 ` Thomas Gleixner
2021-08-14 7:22 ` Paolo Bonzini
2021-08-18 9:32 ` Vitaly Kuznetsov
2021-08-18 20:49 ` Paolo Bonzini
2021-08-06 10:07 ` [v2 PATCH 4/4] x86/kvm: Add guest " Hikaru Nishida
2021-08-10 15:48 ` Thomas Gleixner [this message]
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=87lf59qp1p.ffs@tglx \
--to=tglx@linutronix.de \
--cc=bp@alien8.de \
--cc=dme@dme.org \
--cc=hikalium@chromium.org \
--cc=hpa@zytor.com \
--cc=jgross@suse.com \
--cc=jmattson@google.com \
--cc=john.stultz@linaro.org \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=laijs@linux.alibaba.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mike.travis@hpe.com \
--cc=mingo@redhat.com \
--cc=mlevitsk@redhat.com \
--cc=pbonzini@redhat.com \
--cc=peterz@infradead.org \
--cc=sboyd@kernel.org \
--cc=seanjc@google.com \
--cc=suleiman@google.com \
--cc=thomas.lendacky@amd.com \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
--cc=x86@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).