From: Marc Zyngier <maz@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-kernel@vger.kernel.org, aleksandar.qemu.devel@gmail.com,
alexandru.elisei@arm.com, anup.patel@wdc.com,
aou@eecs.berkeley.edu, atish.patra@wdc.com,
benh@kernel.crashing.org, borntraeger@linux.ibm.com,
bp@alien8.de, catalin.marinas@arm.com, chenhuacai@kernel.org,
dave.hansen@linux.intel.com, david@redhat.com,
frankja@linux.ibm.com, frederic@kernel.org, gor@linux.ibm.com,
hca@linux.ibm.com, imbrenda@linux.ibm.com, james.morse@arm.com,
jmattson@google.com, joro@8bytes.org, kvm@vger.kernel.org,
mingo@redhat.com, mpe@ellerman.id.au, nsaenzju@redhat.com,
palmer@dabbelt.com, paulmck@kernel.org, paulus@samba.org,
paul.walmsley@sifive.com, pbonzini@redhat.com, seanjc@google.com,
suzuki.poulose@arm.com, tglx@linutronix.de,
tsbogend@alpha.franken.de, vkuznets@redhat.com,
wanpengli@tencent.com, will@kernel.org
Subject: Re: [PATCH 1/5] kvm: add exit_to_guest_mode() and enter_from_guest_mode()
Date: Thu, 13 Jan 2022 11:55:11 +0000 [thread overview]
Message-ID: <87pmov97fk.wl-maz@kernel.org> (raw)
In-Reply-To: <YeAGit8JTO/AmAaU@FVFF77S0Q05N>
On Thu, 13 Jan 2022 11:01:30 +0000,
Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Tue, Jan 11, 2022 at 05:54:59PM +0000, Marc Zyngier wrote:
> > Hi Mark,
> >
> > On Tue, 11 Jan 2022 15:35:35 +0000,
> > Mark Rutland <mark.rutland@arm.com> wrote:
[...]
> > > +/*
> > > + * Enter guest context and enter an RCU extended quiescent state.
> > > + *
> > > + * This should be the last thing called before entering the guest, and must be
> > > + * called after any potential use of RCU (including any potentially
> > > + * instrumented code).
> >
> > nit: "the last thing called" is terribly ambiguous. Any architecture
> > obviously calls a ****load of stuff after this point. Should this be
> > 'the last thing involving RCU' instead?
>
> I agree this is unclear and I struggled to fing good wording for this. Is the
> following any better?
>
> /*
> * Enter guest context and enter an RCU extended quiescent state.
> *
> * Between guest_context_enter_irqoff() and guest_context_exit_irqoff() it is
> * unsafe to use any code which may directly or indirectly use RCU, tracing
> * (including IRQ flag tracing), or lockdep. All code in this period must be
> * non-instrumentable.
> */
>
> If that's good I can add similar to guest_context_exit_irqoff().
Yes, that's much clearer, thanks.
>
> [...]
>
> > > +/**
> > > + * exit_to_guest_mode - Fixup state when exiting to guest mode
> > > + *
> > > + * This is analagous to exit_to_user_mode(), and ensures we perform the
> > > + * following in order:
> > > + *
> > > + * 1) Trace interrupts on state
> > > + * 2) Invoke context tracking if enabled to adjust RCU state
> > > + * 3) Tell lockdep that interrupts are enabled
> >
> > nit: or rather, are about to be enabled? Certainly on arm64, the
> > enable happens much later, right at the point where we enter the guest
> > for real.
>
> True; I'd cribbed the wording from the comment block above exit_to_user_mode(),
> but I stripped the context that made that clear. I'll make that:
>
> /**
> * exit_to_guest_mode - Fixup state when exiting to guest mode
> *
> * Entry to a guest will enable interrupts, but the kernel state is
> * interrupts disabled when this is invoked. Also tell RCU about it.
> *
> * 1) Trace interrupts on state
> * 2) Invoke context tracking if enabled to adjust RCU state
> * 3) Tell lockdep that interrupts are enabled
> *
> * Invoked from architecture specific code before entering a guest.
> * Must be called with interrupts disabled and the caller must be
> * non-instrumentable.
> * The caller has to invoke guest_timing_enter_irqoff() before this.
> *
> * Note: this is analagous to exit_to_user_mode().
nit: analogous
> */
>
> ... with likewise for enter_from_guest_mode(), if that's clear enough?
Yes, that's great.
Thanks again,
M.
--
Without deviation from the norm, progress is not possible.
next prev parent reply other threads:[~2022-01-13 11:55 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-11 15:35 [PATCH 0/5] kvm: fix latent guest entry/exit bugs Mark Rutland
2022-01-11 15:35 ` [PATCH 1/5] kvm: add exit_to_guest_mode() and enter_from_guest_mode() Mark Rutland
2022-01-11 17:54 ` Marc Zyngier
2022-01-13 11:01 ` Mark Rutland
2022-01-13 11:55 ` Marc Zyngier [this message]
2022-01-13 13:01 ` Mark Rutland
2022-01-13 20:32 ` Sean Christopherson
2022-01-14 11:48 ` Mark Rutland
2022-01-14 16:11 ` Sean Christopherson
2022-01-18 13:01 ` Mark Rutland
2022-01-11 15:35 ` [PATCH 2/5] kvm/arm64: rework guest entry logic Mark Rutland
2022-01-11 17:55 ` Marc Zyngier
2022-01-13 11:17 ` Mark Rutland
2022-01-13 11:43 ` Marc Zyngier
2022-01-13 12:58 ` Mark Rutland
2022-01-11 15:35 ` [PATCH 3/5] kvm/mips: " Mark Rutland
2022-01-11 15:35 ` [PATCH 4/5] kvm/riscv: " Mark Rutland
2022-01-11 15:35 ` [PATCH 5/5] kvm/x86: " Mark Rutland
2022-01-13 20:50 ` Sean Christopherson
2022-01-14 12:05 ` Mark Rutland
2022-01-14 16:49 ` Sean Christopherson
2022-01-11 18:47 ` [PATCH 0/5] kvm: fix latent guest entry/exit bugs Palmer Dabbelt
2022-01-13 15:20 ` Christian Borntraeger
2022-01-14 12:19 ` Mark Rutland
2022-01-14 12:29 ` Christian Borntraeger
2022-01-14 13:32 ` Mark Rutland
2022-01-14 13:51 ` Christian Borntraeger
2022-01-14 15:19 ` Mark Rutland
2022-01-17 17:45 ` Paolo Bonzini
2022-01-18 12:02 ` Mark Rutland
2022-01-18 12:08 ` Christian Borntraeger
2022-01-18 12:42 ` Christian Borntraeger
2022-01-18 13:12 ` Mark Rutland
2022-01-18 14:15 ` Christian Borntraeger
2022-01-18 15:43 ` Mark Rutland
2022-01-18 16:09 ` Sven Schnelle
2022-01-18 17:50 ` Mark Rutland
2022-01-18 18:12 ` Mark Rutland
2022-01-19 6:41 ` Sven Schnelle
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