linux-kernel - Re: [PATCH] KVM: arm64: fix u64_replace

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Message-ID: <86frf39kh6.wl-maz@kernel.org>
Date: Fri, 11 Jul 2025 09:53:41 +0100
From: Marc Zyngier <maz@...nel.org>
To: "Arnd Bergmann" <arnd@...db.de>
Cc: "Arnd Bergmann" <arnd@...nel.org>,
	"Oliver Upton" <oliver.upton@...ux.dev>,
	"Catalin Marinas" <catalin.marinas@....com>,
	"Will Deacon" <will@...nel.org>,
	"Joey Gouly" <joey.gouly@....com>,
	"Suzuki K Poulose" <suzuki.poulose@....com>,
	"Zenghui Yu" <yuzenghui@...wei.com>,
	"Mark Brown" <broonie@...nel.org>,
	"James Morse" <james.morse@....com>,
	"Sebastian Ott" <sebott@...hat.com>,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: fix u64_replace_bits() usage

On Fri, 11 Jul 2025 09:44:23 +0100,
"Arnd Bergmann" <arnd@...db.de> wrote:
> 
> On Fri, Jul 11, 2025, at 10:36, Marc Zyngier wrote:
> > On Fri, 11 Jul 2025 08:27:47 +0100, Arnd Bergmann <arnd@...nel.org> wrote:
> >>  	if (hpmn > vcpu->kvm->arch.nr_pmu_counters) {
> >>  		hpmn = vcpu->kvm->arch.nr_pmu_counters;
> >> -		u64_replace_bits(val, hpmn, MDCR_EL2_HPMN);
> >> +		val = u64_replace_bits(val, hpmn, MDCR_EL2_HPMN);
> >>  	}
> >>  
> >>  	__vcpu_assign_sys_reg(vcpu, MDCR_EL2, val);
> >
> > This is only in -next, right? Because I have a fix for this already
> > queued for 6.16, as per [1].
> 
> Yes, as far as I can tell, the warning only showed up in linux-next
> after f66f9c3d09c1 ("bitfield: Ensure the return values of helper
> functions are checked").
> 
> As far as I can tell, Ben added the check in linux/bitfield.h
> when he sent you his version of the fix, they just ended up
> in linux-next in the wrong order, so I ended up recreating his
> original fix slightly differently.

I don't think Ben's fix is in -next, as I queued it in the kvmarm
fixes branch, which isn't pulled by -next.

Hopefully Paolo will send this to Linus shortly (pull request
here[1]), and -next will be clean again.

Thanks,

	M.

[1] https://lore.kernel.org/r/20250711084835.2411230-1-maz@kernel.org

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