Re: [PATCH 3/3] KVM: arm64: Skip break phase when we have FEAT_BBM level 2

From: Oliver Upton <oliver.upton@linux.dev>
To: Will Deacon <will@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>,
	Colton Lewis <coltonlewis@google.com>,
	kvm@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev
Subject: Re: [PATCH 3/3] KVM: arm64: Skip break phase when we have FEAT_BBM level 2
Date: Fri, 9 Jun 2023 14:59:50 +0000	[thread overview]
Message-ID: <ZIM+ZgFji/H3Y/9U@linux.dev> (raw)
In-Reply-To: <20230608172112.GA1606@willie-the-truck>

Hey Will,

On Thu, Jun 08, 2023 at 06:21:13PM +0100, Will Deacon wrote:
> > IIRC, Colton was testing largely with permission relaxation, and had
> > forward progress issues b.c. the stale TLB entry was never invalidated
> > in response to a permission fault.
> 
> Would the series at:
> 
> https://lore.kernel.org/r/5d8e1f752051173d2d1b5c3e14b54eb3506ed3ef.1684892404.git-series.apopple@nvidia.com
> 
> help with that?

Heh, that's a rather interesting patch :)

I don't think it is directly related to the problem Colton encounters,
though the symptoms are similar. This crops up when KVM uses a stricter
permission set than the primary MMU, like lazy X for deferred I$
maintenance and write-protection for dirty logging. KVM policy led to
the stale TLB entry, so KVM is the one that needs to initiate the
invalidation.

-- 
Thanks,
Oliver