From: Nuno Das Neves <nunodasneves@linux.microsoft.com>
To: Sean Christopherson <seanjc@google.com>,
Marc Zyngier <maz@kernel.org>,
Oliver Upton <oliver.upton@linux.dev>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Tianrui Zhao <zhaotianrui@loongson.cn>,
Bibo Mao <maobibo@loongson.cn>,
Huacai Chen <chenhuacai@kernel.org>,
Anup Patel <anup@brainfault.org>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Paolo Bonzini <pbonzini@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@kernel.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Neeraj Upadhyay <neeraj.upadhyay@kernel.org>,
Joel Fernandes <joelagnelf@nvidia.com>,
Josh Triplett <josh@joshtriplett.org>,
Boqun Feng <boqun.feng@gmail.com>,
Uladzislau Rezki <urezki@gmail.com>
Cc: linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
kvm@vger.kernel.org, loongarch@lists.linux.dev,
kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org,
linux-hyperv@vger.kernel.org, rcu@vger.kernel.org,
Mukesh R <mrathor@linux.microsoft.com>
Subject: Re: [PATCH v2 1/7] Drivers: hv: Handle NEED_RESCHED_LAZY before transferring to guest
Date: Thu, 28 Aug 2025 16:56:20 -0700 [thread overview]
Message-ID: <0b4eb0cc-657f-4cdb-8255-e3b8f6b14077@linux.microsoft.com> (raw)
In-Reply-To: <20250828000156.23389-2-seanjc@google.com>
On 8/27/2025 5:01 PM, Sean Christopherson wrote:
> Check for NEED_RESCHED_LAZY, not just NEED_RESCHED, prior to transferring
> control to a guest. Failure to check for lazy resched can unnecessarily
> delay rescheduling until the next tick when using a lazy preemption model.
>
> Note, ideally both the checking and processing of TIF bits would be handled
> in common code, to avoid having to keep three separate paths synchronized,
> but defer such cleanups to the future to keep the fix as standalone as
> possible.
>
> Cc: Nuno Das Neves <nunodasneves@linux.microsoft.com>
> Cc: Mukesh R <mrathor@linux.microsoft.com>
> Fixes: 621191d709b1 ("Drivers: hv: Introduce mshv_root module to expose /dev/mshv to VMMs")
> Fixes: 64503b4f4468 ("Drivers: hv: Introduce mshv_vtl driver")
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> drivers/hv/mshv_common.c | 2 +-
> drivers/hv/mshv_root_main.c | 3 ++-
> drivers/hv/mshv_vtl_main.c | 3 ++-
> 3 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/hv/mshv_common.c b/drivers/hv/mshv_common.c
> index 6f227a8a5af7..eb3df3e296bb 100644
> --- a/drivers/hv/mshv_common.c
> +++ b/drivers/hv/mshv_common.c
> @@ -151,7 +151,7 @@ int mshv_do_pre_guest_mode_work(ulong th_flags)
> if (th_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
> return -EINTR;
>
> - if (th_flags & _TIF_NEED_RESCHED)
> + if (th_flags & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY))
> schedule();
>
> if (th_flags & _TIF_NOTIFY_RESUME)
> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
> index 932932cb91ea..0d849f09160a 100644
> --- a/drivers/hv/mshv_root_main.c
> +++ b/drivers/hv/mshv_root_main.c
> @@ -484,7 +484,8 @@ mshv_vp_wait_for_hv_kick(struct mshv_vp *vp)
> static int mshv_pre_guest_mode_work(struct mshv_vp *vp)
> {
> const ulong work_flags = _TIF_NOTIFY_SIGNAL | _TIF_SIGPENDING |
> - _TIF_NEED_RESCHED | _TIF_NOTIFY_RESUME;
> + _TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY |
> + _TIF_NOTIFY_RESUME;
> ulong th_flags;
>
> th_flags = read_thread_flags();
> diff --git a/drivers/hv/mshv_vtl_main.c b/drivers/hv/mshv_vtl_main.c
> index dc6594ae03ad..12f5e77b7095 100644
> --- a/drivers/hv/mshv_vtl_main.c
> +++ b/drivers/hv/mshv_vtl_main.c
> @@ -728,7 +728,8 @@ static int mshv_vtl_ioctl_return_to_lower_vtl(void)
> preempt_disable();
> for (;;) {
> const unsigned long VTL0_WORK = _TIF_SIGPENDING | _TIF_NEED_RESCHED |
> - _TIF_NOTIFY_RESUME | _TIF_NOTIFY_SIGNAL;
> + _TIF_NOTIFY_RESUME | _TIF_NOTIFY_SIGNAL |
> + _TIF_NEED_RESCHED_LAZY;
> unsigned long ti_work;
> u32 cancel;
> unsigned long irq_flags;
Tested by compiling with CONFIG_PREEMPT_LAZY=y and booting a guest. For
the test I added a check to confirm _TIF_NEED_RESCHED_LAZY was set and
honored.
Looks good, thanks.
Tested-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Reviewed-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
next prev parent reply other threads:[~2025-08-28 23:56 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-28 0:01 [PATCH v2 0/7] Drivers: hv: Fix NEED_RESCHED_LAZY and use common APIs Sean Christopherson
2025-08-28 0:01 ` [PATCH v2 1/7] Drivers: hv: Handle NEED_RESCHED_LAZY before transferring to guest Sean Christopherson
2025-08-28 23:56 ` Nuno Das Neves [this message]
2025-08-28 0:01 ` [PATCH v2 2/7] Drivers: hv: Disentangle VTL return cancellation from SIGPENDING Sean Christopherson
2025-08-29 18:38 ` Wei Liu
2025-08-28 0:01 ` [PATCH v2 3/7] Drivers: hv: Disable IRQs only after handling pending work before VTL return Sean Christopherson
2025-08-28 0:01 ` [PATCH v2 4/7] entry/kvm: KVM: Move KVM details related to signal/-EINTR into KVM proper Sean Christopherson
2025-09-02 15:41 ` Thomas Gleixner
2025-08-28 0:01 ` [PATCH v2 5/7] entry: Rename "kvm" entry code assets to "virt" to genericize APIs Sean Christopherson
2025-09-02 15:41 ` Thomas Gleixner
2025-08-28 0:01 ` [PATCH v2 6/7] Drivers: hv: Use common "entry virt" APIs to do work in root before running guest Sean Christopherson
2025-08-29 0:03 ` Nuno Das Neves
2025-08-28 0:01 ` [PATCH v2 7/7] Drivers: hv: Use "entry virt" APIs to do work before returning to lower VTL Sean Christopherson
2025-09-04 23:41 ` [PATCH v2 0/7] Drivers: hv: Fix NEED_RESCHED_LAZY and use common APIs Wei Liu
2025-09-05 5:39 ` Sean Christopherson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=0b4eb0cc-657f-4cdb-8255-e3b8f6b14077@linux.microsoft.com \
--to=nunodasneves@linux.microsoft.com \
--cc=anup@brainfault.org \
--cc=aou@eecs.berkeley.edu \
--cc=boqun.feng@gmail.com \
--cc=bp@alien8.de \
--cc=catalin.marinas@arm.com \
--cc=chenhuacai@kernel.org \
--cc=dave.hansen@linux.intel.com \
--cc=decui@microsoft.com \
--cc=frederic@kernel.org \
--cc=haiyangz@microsoft.com \
--cc=joelagnelf@nvidia.com \
--cc=josh@joshtriplett.org \
--cc=kvm-riscv@lists.infradead.org \
--cc=kvm@vger.kernel.org \
--cc=kvmarm@lists.linux.dev \
--cc=kys@microsoft.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-hyperv@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-riscv@lists.infradead.org \
--cc=loongarch@lists.linux.dev \
--cc=luto@kernel.org \
--cc=maobibo@loongson.cn \
--cc=maz@kernel.org \
--cc=mingo@redhat.com \
--cc=mrathor@linux.microsoft.com \
--cc=neeraj.upadhyay@kernel.org \
--cc=oliver.upton@linux.dev \
--cc=palmer@dabbelt.com \
--cc=paul.walmsley@sifive.com \
--cc=paulmck@kernel.org \
--cc=pbonzini@redhat.com \
--cc=peterz@infradead.org \
--cc=rcu@vger.kernel.org \
--cc=seanjc@google.com \
--cc=tglx@linutronix.de \
--cc=urezki@gmail.com \
--cc=wei.liu@kernel.org \
--cc=will@kernel.org \
--cc=x86@kernel.org \
--cc=zhaotianrui@loongson.cn \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).