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From: Vasily Gorbik <gor@linux.ibm.com>
To: Sven Schnelle <svens@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
	Sean Christopherson <seanjc@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Michael Tokarev <mjt@tls.msk.ru>,
	Heiko Carstens <heiko.carstens@de.ibm.com>
Subject: Re: [PATCH v3 9/9] KVM: Move instrumentation-safe annotations for enter/exit to x86 code
Date: Fri, 23 Apr 2021 11:32:34 +0200	[thread overview]
Message-ID: <your-ad-here.call-01619170354-ext-2090@work.hours> (raw)
In-Reply-To: <yt9d4kfypeov.fsf@linux.ibm.com>

On Thu, Apr 22, 2021 at 04:38:24PM +0200, Sven Schnelle wrote:
> Christian Borntraeger <borntraeger@de.ibm.com> writes:
> 
> > On 16.04.21 00:21, Sean Christopherson wrote:
> >> Drop the instrumentation_{begin,end}() annonations from the common KVM
> >> guest enter/exit helpers, and massage the x86 code as needed to preserve
> >> the necessary annotations.  x86 is the only architecture whose transition
> >> flow is tagged as noinstr, and more specifically, it is the only
> >> architecture for which instrumentation_{begin,end}() can be non-empty.
> >> No other architecture supports CONFIG_STACK_VALIDATION=y, and s390
> >> is the
> >> only other architecture that support CONFIG_DEBUG_ENTRY=y.  For
> >> instrumentation annontations to be meaningful, both aformentioned configs
> >> must be enabled.
> >> Letting x86 deal with the annotations avoids unnecessary nops by
> >> squashing back-to-back instrumention-safe sequences.
> >
> > We have considered implementing objtool for s390. Not sure where we
> > stand and if we will do this or not. Sven/Heiko?
> 
> We are planning to support objtool on s390. Vasily is working on it -
> maybe he has some thoughts about this.

We got CONFIG_DEBUG_ENTRY=y since 5.12, objtool runs on vmlinux.o but I have
not yet enabled --noinstr option in s390 objtool. So, it's hard to say in
advance if this particular change would make things better or worse.
In general, common code annotations are problematic, because arch
specific code is still not identical and this leads sometimes to different
needs for common code annotations.

I'll try to experiment with --noinstr on s390 shortly.

  reply	other threads:[~2021-04-23  9:33 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-15 22:20 [PATCH v3 0/9] KVM: Fix tick-based accounting for x86 guests Sean Christopherson
2021-04-15 22:20 ` [PATCH v3 1/9] context_tracking: Move guest exit context tracking to separate helpers Sean Christopherson
2021-04-20 18:48   ` Christian Borntraeger
2021-04-21 10:57   ` Frederic Weisbecker
2021-04-15 22:20 ` [PATCH v3 2/9] context_tracking: Move guest exit vtime accounting " Sean Christopherson
2021-04-20 18:48   ` Christian Borntraeger
2021-04-15 22:21 ` [PATCH v3 3/9] KVM: x86: Defer tick-based accounting 'til after IRQ handling Sean Christopherson
2021-04-20 23:14   ` Frederic Weisbecker
2021-04-20 23:26     ` Sean Christopherson
2021-04-21 10:11       ` Frederic Weisbecker
2021-04-21 12:19       ` Frederic Weisbecker
2021-04-28 22:38         ` Sean Christopherson
2021-04-21 10:07   ` Frederic Weisbecker
2021-04-15 22:21 ` [PATCH v3 4/9] sched/vtime: Move vtime accounting external declarations above inlines Sean Christopherson
2021-04-21  7:02   ` Christian Borntraeger
2021-04-15 22:21 ` [PATCH v3 5/9] sched/vtime: Move guest enter/exit vtime accounting to vtime.h Sean Christopherson
2021-04-15 22:21 ` [PATCH v3 6/9] context_tracking: Consolidate guest enter/exit wrappers Sean Christopherson
2021-04-15 22:21 ` [PATCH v3 7/9] context_tracking: KVM: Move guest enter/exit wrappers to KVM's domain Sean Christopherson
2021-04-21  7:10   ` Christian Borntraeger
2021-04-15 22:21 ` [PATCH v3 8/9] KVM: x86: Consolidate guest enter/exit logic to common helpers Sean Christopherson
2021-04-15 22:21 ` [PATCH v3 9/9] KVM: Move instrumentation-safe annotations for enter/exit to x86 code Sean Christopherson
2021-04-21  8:09   ` Christian Borntraeger
2021-04-22 14:38     ` Sven Schnelle
2021-04-23  9:32       ` Vasily Gorbik [this message]
2021-04-20 23:33 ` [PATCH v3 0/9] KVM: Fix tick-based accounting for x86 guests Frederic Weisbecker

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