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From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
	Andy Lutomirski <luto@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Marc Zyngier <maz@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	kvm@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-s390 <linux-s390@vger.kernel.org>
Subject: Re: [RFC patch 00/15] entry: Provide generic implementation for host and guest entry/exit work
Date: Tue, 24 Sep 2019 08:50:20 +0200	[thread overview]
Message-ID: <ae5c6329-4ddf-2243-3a86-fbfdfd029918@de.ibm.com> (raw)
In-Reply-To: <20190919150314.054351477@linutronix.de>



On 19.09.19 17:03, Thomas Gleixner wrote:
> When working on a way to move out the posix cpu timer expiry out of the
> timer interrupt context, I noticed that KVM is not handling pending task
> work before entering a guest. A quick hack was to add that to the x86 KVM
> handling loop. The discussion ended with a request to make this a generic
> infrastructure possible with also moving the per arch implementations of
> the enter from and return to user space handling generic.
> 
>   https://lore.kernel.org/r/89E42BCC-47A8-458B-B06A-D6A20D20512C@amacapital.net
> 
> You asked for it, so don't complain that you have to review it :)
> 
> The series implements the syscall enter/exit and the general exit to
> userspace work handling along with the pre guest enter functionality.
> 
> The series converts x86 and ARM64. x86 is fully tested including selftests
> etc. ARM64 is only compile tested for now as my only ARM64 testbox is not
> available right now.

It seems that s390x would also need to look into TIF_NOTIFY_PENDING before
entering a KVM guest. Given that the s390x entry path is still in assembler
this might not be something to do quickly.

Would it make sense to actually start with a minimal solution (e.g. one that
provides notify_resume_pending like your original patch) as a fix. That would
also be simple to backport. And then we can do the proper rework on top.

Or do we consider anything that depends on TIF_NOTIFY_PENDING before entering
a guest as not important enough for stable?
After all the vcpu_run ioctl almost never returns to userspace and nothing 
was obviously broken.

Another question: Are there callbacks due to TIF_NOTIFY_PENDING that should
NOT happen as long as we stay in the vpcu loop?


      parent reply	other threads:[~2019-09-24  6:50 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-19 15:03 [RFC patch 00/15] entry: Provide generic implementation for host and guest entry/exit work Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 01/15] entry: Provide generic syscall entry functionality Thomas Gleixner
2019-09-20 23:38   ` Andy Lutomirski
2019-10-20 11:49     ` Thomas Gleixner
2019-09-23  9:05   ` Mike Rapoport
2019-09-19 15:03 ` [RFC patch 02/15] x86/entry: Remove _TIF_NOHZ from _TIF_WORK_SYSCALL_ENTRY Thomas Gleixner
2019-09-20 23:39   ` Andy Lutomirski
2019-09-23 20:43     ` Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 03/15] x86/entry: Use generic syscall entry function Thomas Gleixner
2019-09-20 23:41   ` Andy Lutomirski
2019-09-23  8:31     ` Peter Zijlstra
2019-09-23  8:40       ` Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 04/15] arm64/entry: " Thomas Gleixner
2019-09-20 12:21   ` Catalin Marinas
2019-09-19 15:03 ` [RFC patch 05/15] entry: Provide generic syscall exit function Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 06/15] x86/entry: Use generic syscall exit functionality Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 07/15] arm64/syscall: Remove obscure flag check Thomas Gleixner
2019-09-20 14:29   ` Catalin Marinas
2019-09-19 15:03 ` [RFC patch 08/15] arm64/syscall: Use generic syscall exit functionality Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 09/15] entry: Provide generic exit to usermode functionality Thomas Gleixner
2019-09-23  8:30   ` Peter Zijlstra
2019-09-19 15:03 ` [RFC patch 10/15] x86/entry: Move irq tracing to C code Thomas Gleixner
2019-09-23  8:47   ` Peter Zijlstra
2019-09-23 10:27     ` Thomas Gleixner
2019-09-23 11:49       ` Peter Zijlstra
2019-09-23 11:55         ` Peter Zijlstra
2019-09-23 12:10           ` Peter Zijlstra
2019-09-23 17:24             ` Andy Lutomirski
2019-09-26  2:59   ` Josh Poimboeuf
2019-09-19 15:03 ` [RFC patch 11/15] x86/entry: Use generic exit to usermode Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 12/15] arm64/entry: " Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 13/15] arm64/entry: Move FPU restore out of exit_to_usermode() loop Thomas Gleixner
2019-09-19 15:03 ` [RFC patch 14/15] workpending: Provide infrastructure for work before entering a guest Thomas Gleixner
2019-09-19 15:40   ` Paolo Bonzini
2019-09-20 11:48     ` Thomas Gleixner
2019-09-23 18:17   ` Andy Lutomirski
2019-09-26 11:35   ` Miroslav Benes
2019-09-19 15:03 ` [RFC patch 15/15] x86/kvm: Use GENERIC_EXIT_WORKPENDING Thomas Gleixner
2019-09-19 15:40   ` Paolo Bonzini
2019-09-20 15:12 ` [RFC patch 00/15] entry: Provide generic implementation for host and guest entry/exit work Mark Rutland
2019-09-23 20:50   ` Thomas Gleixner
2019-09-23 18:18 ` Andy Lutomirski
2019-09-24  6:50 ` Christian Borntraeger [this message]

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