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From:   Oliver Upton <oliver.upton@linux.dev>
To:     Ricardo Koller <ricarkol@google.com>
Cc:     Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        kvm@vger.kernel.org, kvmarm@lists.linux.dev,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] KVM: arm64: Don't serialize if the access flag isn't
 set
Message-ID: <Y4Z2aWVEnluy+d3+@google.com>
References: <20221129191946.1735662-1-oliver.upton@linux.dev>
 <20221129191946.1735662-3-oliver.upton@linux.dev>
 <Y4Zw/J3srTsZ57P7@google.com>
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Hi Ricardo,

Thanks for having a look.

On Tue, Nov 29, 2022 at 12:52:12PM -0800, Ricardo Koller wrote:
> On Tue, Nov 29, 2022 at 07:19:44PM +0000, Oliver Upton wrote:

[...]

> > +	ret = stage2_update_leaf_attrs(pgt, addr, 1, KVM_PTE_LEAF_ATTR_LO_S2_AF, 0,
> > +				       &pte, NULL, 0);
> > +	if (!ret)
> > +		dsb(ishst);
> 
> At the moment, the only reason for stage2_update_leaf_attrs() to not
> update the PTE is if it's not valid:
> 
> 	if (!kvm_pte_valid(pte))
> 			return 0;
> 
> I guess you could check that as well:
> 
> +	if (!ret || kvm_pte_valid(pte))
> +		dsb(ishst);

Thanks for catching this.

Instead of pivoting on the returned PTE value, how about we return
-EAGAIN from the early return in stage2_attr_walker()? It would better
match the pattern used elsewhere in the pgtable code.

--
Thanks,
Oliver