From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Dexuan Cui <decui@microsoft.com>
Cc: "linux-arch\@vger.kernel.org" <linux-arch@vger.kernel.org>,
"arnd\@arndb.de" <arnd@arndb.de>, "bp\@alien8.de" <bp@alien8.de>,
"daniel.lezcano\@linaro.org" <daniel.lezcano@linaro.org>,
Haiyang Zhang <haiyangz@microsoft.com>,
"hpa\@zytor.com" <hpa@zytor.com>,
KY Srinivasan <kys@microsoft.com>,
"linux-hyperv\@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"mingo\@redhat.com" <mingo@redhat.com>,
"sashal\@kernel.org" <sashal@kernel.org>,
Stephen Hemminger <sthemmin@microsoft.com>,
"tglx\@linutronix.de" <tglx@linutronix.de>,
"x86\@kernel.org" <x86@kernel.org>,
Michael Kelley <mikelley@microsoft.com>,
Sasha Levin <Alexander.Levin@microsoft.com>
Subject: RE: [PATCH v5 1/3] x86/hyper-v: Suspend/resume the hypercall page for hibernation
Date: Fri, 27 Sep 2019 11:05:24 +0200 [thread overview]
Message-ID: <877e5u6re3.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <PU1P153MB01695A159E9843B4E1EC13AEBF810@PU1P153MB0169.APCP153.PROD.OUTLOOK.COM>
Dexuan Cui <decui@microsoft.com> writes:
>> From: Vitaly Kuznetsov <vkuznets@redhat.com>
>> Sent: Thursday, September 26, 2019 3:44 AM
>> > [...]
>> > +static int hv_suspend(void)
>> > +{
>> > + union hv_x64_msr_hypercall_contents hypercall_msr;
>> > +
>> > + /* Reset the hypercall page */
>> > + rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
>> > + hypercall_msr.enable = 0;
>> > + wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
>> > +
>>
>> (trying to think out loud, not sure there's a real issue):
>>
>> When PV IPIs (or PV TLB flush) are enabled we do the following checks:
>>
>> if (!hv_hypercall_pg)
>> return false;
>>
>> or
>> if (!hv_hypercall_pg)
>> goto do_native;
>>
>> which will pass as we're not invalidating the pointer. Can we actually
>> be sure that the kernel will never try to send an IPI/do TLB flush
>> before we resume?
>>
>> Vitaly
>
> When hv_suspend() and hv_resume() are called by syscore_suspend()
> and syscore_resume(), respectively, all the non-boot CPUs are disabled and
> only CPU0 is active and interrupts are disabled, e.g. see
>
> hibernate() ->
> hibernation_snapshot() ->
> create_image() ->
> suspend_disable_secondary_cpus()
> local_irq_disable()
>
> syscore_suspend()
> swsusp_arch_suspend
> syscore_resume
>
> local_irq_enable
> enable_nonboot_cpus
>
>
> So, I'm pretty sure no IPI can happen between hv_suspend() and hv_resume().
> self-IPI is not supposed to happen either, since interrupts are disabled.
>
> IMO TLB flush should not be an issue either, unless the kernel changes page
> tables between hv_suspend() and hv_resume(), which is not the case as I
> checked the related code, but it looks in theory that might happen, say, in
> the future, so if you insist we should save the variable "hv_hypercall_pg"
> to a temporary variable and set the "hv_hypercall_pg" to NULL before we
> disable the hypercall page
Let's do it as a future proof so we can keep relying on !hv_hypercall_pg
everywhere we need. No need to change this patch IMO, a follow-up would
do.
--
Vitaly
next prev parent reply other threads:[~2019-09-27 9:05 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-05 22:47 [PATCH v5 0/3] Enhance Hyper-V for hibernation Dexuan Cui
2019-09-05 22:47 ` [PATCH v5 1/3] x86/hyper-v: Suspend/resume the hypercall page " Dexuan Cui
2019-09-26 10:44 ` Vitaly Kuznetsov
2019-09-27 6:48 ` Dexuan Cui
2019-09-27 9:05 ` Vitaly Kuznetsov [this message]
2019-09-30 18:49 ` Dexuan Cui
2019-09-05 22:47 ` [PATCH v5 2/3] x86/hyper-v: Implement hv_is_hibernation_supported() Dexuan Cui
2019-09-05 22:47 ` [PATCH v5 3/3] clocksource/drivers: Suspend/resume Hyper-V clocksource for hibernation Dexuan Cui
2019-09-25 23:21 ` Daniel Lezcano
2019-09-25 23:35 ` Dexuan Cui
2019-09-26 13:16 ` Daniel Lezcano
2019-09-27 5:57 ` Dexuan Cui
2019-09-25 22:49 ` [PATCH v5 0/3] Enhance Hyper-V " Dexuan Cui
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