linux-kernel - [PATCH 2/5] Drivers: hv: Handle NEED_RESCHED

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Message-ID: <20250825200622.3759571-3-seanjc@google.com>
Date: Mon, 25 Aug 2025 13:06:19 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Tianrui Zhao <zhaotianrui@...ngson.cn>, Bibo Mao <maobibo@...ngson.cn>, 
	Huacai Chen <chenhuacai@...nel.org>, Anup Patel <anup@...infault.org>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Sean Christopherson <seanjc@...gle.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"K. Y. Srinivasan" <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, 
	Dexuan Cui <decui@...rosoft.com>, Peter Zijlstra <peterz@...radead.org>, 
	Andy Lutomirski <luto@...nel.org>, "Paul E. McKenney" <paulmck@...nel.org>, 
	Frederic Weisbecker <frederic@...nel.org>, Neeraj Upadhyay <neeraj.upadhyay@...nel.org>, 
	Joel Fernandes <joelagnelf@...dia.com>, Josh Triplett <josh@...htriplett.org>, 
	Boqun Feng <boqun.feng@...il.com>, Uladzislau Rezki <urezki@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, kvm@...r.kernel.org, loongarch@...ts.linux.dev, 
	kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org, 
	linux-hyperv@...r.kernel.org, rcu@...r.kernel.org
Subject: [PATCH 2/5] Drivers: hv: Handle NEED_RESCHED_LAZY before transferring
 to guest

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.

Fixes: 621191d709b1 ("Drivers: hv: Introduce mshv_root module to expose /dev/mshv to VMMs")
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 drivers/hv/mshv_common.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/mshv_common.c b/drivers/hv/mshv_common.c
index 1acc47c4be0d..b953b5e21110 100644
--- a/drivers/hv/mshv_common.c
+++ b/drivers/hv/mshv_common.c
@@ -151,7 +151,7 @@ static 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)
@@ -163,7 +163,8 @@ static int __mshv_do_pre_guest_mode_work(ulong th_flags)
 int mshv_do_pre_guest_mode_work(void)
 {
 	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();
-- 
2.51.0.261.g7ce5a0a67e-goog