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From: Miklos Szeredi <miklos@szeredi.hu>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	x86@kernel.org, Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Andy Lutomirski <luto@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Juergen Gross <jgross@suse.com>,
	Christophe Leroy <christophe.leroy@c-s.fr>
Subject: Re: [patch 0/3] vdso: Unbreak VDSO with PV and HyperV clocksources
Date: Tue, 9 Jun 2020 15:10:15 +0200	[thread overview]
Message-ID: <CAJfpegtgQZvjjapsgQsG6AGGmNsHoGaczVc9=nw941a4-atmGw@mail.gmail.com> (raw)
In-Reply-To: <20200606215114.380723277@linutronix.de>

On Sun, Jun 7, 2020 at 11:36 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> Miklos reported [1] that the recent VDSO changes broke paravirt clocksource
> based VDSO in the case that the clocksource is invalidated by the
> hypervisor which happens after a suspend/resume cycle of the host.
>
> The result is a stale clocksource which is about 2200 seconds ahead of the
> actual time and jumps forward by 2200 seconds once 2200 seconds have
> elapsed.
>
> The reason for this is the core code change which optimized the VDSO
> clocksource validation by checking for the clocksource mode instead of
> using the rather subtle check for the clocksource read return value whether
> it has bit 63 set.
>
> For some reason my brain blanked when doing that change, even if I should
> have known better.
>
> The following series restores the previous behaviour but preserves the
> initially intended optimization for architectures which don't need that PV
> handling.

Thanks for fixing.

Tested-by: Miklos Szeredi <mszeredi@redhat.com>

Miklos

      parent reply	other threads:[~2020-06-09 13:10 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-06 21:51 Thomas Gleixner
2020-06-06 21:51 ` [patch 1/3] clocksource: Remove obsolete ifdef Thomas Gleixner
2020-06-09 14:40   ` [tip: x86/urgent] " tip-bot2 for Thomas Gleixner
2020-06-06 21:51 ` [patch 2/3] lib/vdso: Provide sanity check for cycles (again) Thomas Gleixner
2020-06-09 14:40   ` [tip: x86/urgent] " tip-bot2 for Thomas Gleixner
2020-06-06 21:51 ` [patch 3/3] x86/vdso: Unbreak paravirt VDSO clocks Thomas Gleixner
2020-06-09 14:40   ` [tip: x86/urgent] " tip-bot2 for Thomas Gleixner
2020-06-09 13:10 ` Miklos Szeredi [this message]

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