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From: Andrew Jones <andrew.jones@linux.dev>
To: kvm-riscv@lists.infradead.org
Cc: anup@brainfault.org, atish.patra@linux.dev, pjw@kernel.org,
	 palmer@dabbelt.com, kvm@vger.kernel.org,
	linux-riscv@lists.infradead.org,  linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] RISC-V: KVM: Convert IMSIC vsfile_lock to a raw spinlock
Date: Mon, 19 Oct 2026 19:16:06 +0200	[thread overview]
Message-ID: <atZPqGKEip_sW3fr@orel> (raw)
In-Reply-To: <20261019134709.2610129-1-andrew.jones@linux.dev>

On Mon, Oct 19, 2026 at 03:47:09PM +0200, Andrew Jones wrote:
> kvm_riscv_vcpu_aia_imsic_put() runs from the scheduler preemption
> notifier with the raw runqueue lock held, so it must not take
> vsfile_lock, an rwlock_t, which sleeps on PREEMPT_RT. All vsfile_lock
> critical sections are short, so a raw spinlock is fine.
> 
> Fixes: 4cec89db80ba ("RISC-V: KVM: Move HGEI[E|P] CSR access to IMSIC virtualization")
> Signed-off-by: Andrew Jones <andrew.jones@linux.dev>
> ---
> v2:
>  - Convert vsfile_lock to raw_spinlock_t instead of adding a separate
>    hgei_lock [Anup]

Hi Anup,

Sashiko found an ABBA deadlock with this v2[1]. Making vsfile_lock
exclusive serializes kvm_riscv_vcpu_aia_imsic_put(), which runs under
rq->__lock, against the SW-file inject paths, which kick the vCPU
(pi_lock/rq->__lock) while holding vsfile_lock. Lockdep confirms it with
an EMUL mode guest, and the host then hangs (I should have tested with
EMUL before...). v1 doesn't have the problem, since its hgei_lock never
has anything that wakes tasks nested under it. I tested v1 in both EMUL
mode and hwaccel mode [again] with lockdep and it's good.

Should we take v1 instead?

[1] https://sashiko.dev/#/patchset/20261019134709.2610129-1-andrew.jones@linux.dev?part=1

Thanks,
drew

-- 
kvm-riscv mailing list
kvm-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kvm-riscv

WARNING: multiple messages have this Message-ID (diff)
From: Andrew Jones <andrew.jones@linux.dev>
To: kvm-riscv@lists.infradead.org
Cc: anup@brainfault.org, atish.patra@linux.dev, pjw@kernel.org,
	 palmer@dabbelt.com, kvm@vger.kernel.org,
	linux-riscv@lists.infradead.org,  linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] RISC-V: KVM: Convert IMSIC vsfile_lock to a raw spinlock
Date: Mon, 19 Oct 2026 19:16:06 +0200	[thread overview]
Message-ID: <atZPqGKEip_sW3fr@orel> (raw)
In-Reply-To: <20261019134709.2610129-1-andrew.jones@linux.dev>

On Mon, Oct 19, 2026 at 03:47:09PM +0200, Andrew Jones wrote:
> kvm_riscv_vcpu_aia_imsic_put() runs from the scheduler preemption
> notifier with the raw runqueue lock held, so it must not take
> vsfile_lock, an rwlock_t, which sleeps on PREEMPT_RT. All vsfile_lock
> critical sections are short, so a raw spinlock is fine.
> 
> Fixes: 4cec89db80ba ("RISC-V: KVM: Move HGEI[E|P] CSR access to IMSIC virtualization")
> Signed-off-by: Andrew Jones <andrew.jones@linux.dev>
> ---
> v2:
>  - Convert vsfile_lock to raw_spinlock_t instead of adding a separate
>    hgei_lock [Anup]

Hi Anup,

Sashiko found an ABBA deadlock with this v2[1]. Making vsfile_lock
exclusive serializes kvm_riscv_vcpu_aia_imsic_put(), which runs under
rq->__lock, against the SW-file inject paths, which kick the vCPU
(pi_lock/rq->__lock) while holding vsfile_lock. Lockdep confirms it with
an EMUL mode guest, and the host then hangs (I should have tested with
EMUL before...). v1 doesn't have the problem, since its hgei_lock never
has anything that wakes tasks nested under it. I tested v1 in both EMUL
mode and hwaccel mode [again] with lockdep and it's good.

Should we take v1 instead?

[1] https://sashiko.dev/#/patchset/20261019134709.2610129-1-andrew.jones@linux.dev?part=1

Thanks,
drew

WARNING: multiple messages have this Message-ID (diff)
From: Andrew Jones <andrew.jones@linux.dev>
To: kvm-riscv@lists.infradead.org
Cc: anup@brainfault.org, atish.patra@linux.dev, pjw@kernel.org,
	 palmer@dabbelt.com, kvm@vger.kernel.org,
	linux-riscv@lists.infradead.org,  linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] RISC-V: KVM: Convert IMSIC vsfile_lock to a raw spinlock
Date: Mon, 19 Oct 2026 19:16:06 +0200	[thread overview]
Message-ID: <atZPqGKEip_sW3fr@orel> (raw)
In-Reply-To: <20261019134709.2610129-1-andrew.jones@linux.dev>

On Mon, Oct 19, 2026 at 03:47:09PM +0200, Andrew Jones wrote:
> kvm_riscv_vcpu_aia_imsic_put() runs from the scheduler preemption
> notifier with the raw runqueue lock held, so it must not take
> vsfile_lock, an rwlock_t, which sleeps on PREEMPT_RT. All vsfile_lock
> critical sections are short, so a raw spinlock is fine.
> 
> Fixes: 4cec89db80ba ("RISC-V: KVM: Move HGEI[E|P] CSR access to IMSIC virtualization")
> Signed-off-by: Andrew Jones <andrew.jones@linux.dev>
> ---
> v2:
>  - Convert vsfile_lock to raw_spinlock_t instead of adding a separate
>    hgei_lock [Anup]

Hi Anup,

Sashiko found an ABBA deadlock with this v2[1]. Making vsfile_lock
exclusive serializes kvm_riscv_vcpu_aia_imsic_put(), which runs under
rq->__lock, against the SW-file inject paths, which kick the vCPU
(pi_lock/rq->__lock) while holding vsfile_lock. Lockdep confirms it with
an EMUL mode guest, and the host then hangs (I should have tested with
EMUL before...). v1 doesn't have the problem, since its hgei_lock never
has anything that wakes tasks nested under it. I tested v1 in both EMUL
mode and hwaccel mode [again] with lockdep and it's good.

Should we take v1 instead?

[1] https://sashiko.dev/#/patchset/20261019134709.2610129-1-andrew.jones@linux.dev?part=1

Thanks,
drew

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

  parent reply	other threads:[~2026-10-19 17:16 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-10-19 13:47 [PATCH v2] RISC-V: KVM: Convert IMSIC vsfile_lock to a raw spinlock Andrew Jones
2026-10-19 13:47 ` Andrew Jones
2026-10-19 13:47 ` Andrew Jones
2026-10-19 13:57 ` sashiko-bot
2026-10-19 17:16 ` Andrew Jones [this message]
2026-10-19 17:16   ` Andrew Jones
2026-10-19 17:16   ` Andrew Jones

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