linux-kernel - Re: [PATCH v2 0/7] Drivers: hv: Fix NEED_RESCHED

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Message-ID: <aLp3makY6FzuUwor@google.com>
Date: Thu, 4 Sep 2025 22:39:37 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Wei Liu <wei.liu@...nel.org>
Cc: 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>, 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>, 
	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>, 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, Nuno Das Neves <nunodasneves@...ux.microsoft.com>, 
	Mukesh R <mrathor@...ux.microsoft.com>
Subject: Re: [PATCH v2 0/7] Drivers: hv: Fix NEED_RESCHED_LAZY and use common APIs

On Thu, Sep 04, 2025, Wei Liu wrote:
> On Wed, Aug 27, 2025 at 05:01:49PM -0700, Sean Christopherson wrote:
> > Fix a bug where MSHV root partitions (and upper-level VTL code) don't honor
> > NEED_RESCHED_LAZY, and then deduplicate the TIF related MSHV code by turning
> > the "kvm" entry APIs into more generic "virt" APIs.
> > 
> > This version is based on
> > 
> >   git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git hyperv-next
> > 
> > in order to pickup the VTL changes that are queued for 6.18.  I also
> > squashed the NEED_RESCHED_LAZY fixes for root and VTL modes into a single
> > patch, as it should be easy/straightforward to drop the VTL change as needed
> > if we want this in 6.17 or earlier.
> > 
> > That effectively means the full series is dependent on the VTL changes being
> > fully merged for 6.18.  But I think that's ok as it's really only the MSHV
> > changes that have any urgency whatsoever, and I assume that Microsoft is
> > the only user that truly cares about the MSHV root fix.  I.e. if the whole
> > thing gets delayed, I think it's only the Hyper-V folks that are impacted.
> > 
> > I have no preference what tree this goes through, or when, and can respin
> > and/or split as needed.
> > 
> > As with v1, the Hyper-V stuff and non-x86 architectures are compile-tested
> > only.
> > 
> > v2:
> >  - Rebase on hyperv-next.
> >  - Fix and converge the VTL code as well. [Peter, Nuno]
> > 
> > v1: https://lore.kernel.org/all/20250825200622.3759571-1-seanjc@google.com
> > 
> 
> I dropped the mshv_vtl changes in this series and applied the rest
> (including the KVM changes) to hyperv-next.

mshv_do_pre_guest_mode_work() ended up getting left behind since its removal was
in the last mshv_vtl patch.

  $ git grep mshv_do_pre_guest_mode_work
  drivers/hv/mshv.h:int mshv_do_pre_guest_mode_work(ulong th_flags);
  drivers/hv/mshv_common.c:int mshv_do_pre_guest_mode_work(ulong th_flags)
  drivers/hv/mshv_common.c:EXPORT_SYMBOL_GPL(mshv_do_pre_guest_mode_work);

Want to squash this into 3786d7d6b3c0 ("mshv: Use common "entry virt" APIs to do
work in root before running guest")?

---
 drivers/hv/mshv.h        |  2 --
 drivers/hv/mshv_common.c | 22 ----------------------
 2 files changed, 24 deletions(-)

diff --git a/drivers/hv/mshv.h b/drivers/hv/mshv.h
index 0340a67acd0a..d4813df92b9c 100644
--- a/drivers/hv/mshv.h
+++ b/drivers/hv/mshv.h
@@ -25,6 +25,4 @@ int hv_call_set_vp_registers(u32 vp_index, u64 partition_id, u16 count,
 int hv_call_get_partition_property(u64 partition_id, u64 property_code,
 				   u64 *property_value);
 
-int mshv_do_pre_guest_mode_work(ulong th_flags);
-
 #endif /* _MSHV_H */
diff --git a/drivers/hv/mshv_common.c b/drivers/hv/mshv_common.c
index eb3df3e296bb..aa2be51979fd 100644
--- a/drivers/hv/mshv_common.c
+++ b/drivers/hv/mshv_common.c
@@ -138,25 +138,3 @@ int hv_call_get_partition_property(u64 partition_id,
 	return 0;
 }
 EXPORT_SYMBOL_GPL(hv_call_get_partition_property);
-
-/*
- * Handle any pre-processing before going into the guest mode on this cpu, most
- * notably call schedule(). Must be invoked with both preemption and
- * interrupts enabled.
- *
- * Returns: 0 on success, -errno on error.
- */
-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 | _TIF_NEED_RESCHED_LAZY))
-		schedule();
-
-	if (th_flags & _TIF_NOTIFY_RESUME)
-		resume_user_mode_work(NULL);
-
-	return 0;
-}
-EXPORT_SYMBOL_GPL(mshv_do_pre_guest_mode_work);

base-commit: 3786d7d6b3c0a412ebe4439ba4a7d4b0e27d9a12
--