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From: Marc Zyngier <maz@kernel.org>
To: Christoffer Dall <christoffer.dall@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v2] KVM: arm64: Don't set HCR_EL2.TVM when S2FWB is supported
Date: Mon, 28 Oct 2019 13:45:49 +0000
Message-ID: <86tv7tx9te.wl-maz@kernel.org> (raw)
In-Reply-To: <20191028130541.30536-1-christoffer.dall@arm.com>

On Mon, 28 Oct 2019 13:05:41 +0000,
Christoffer Dall <christoffer.dall@arm.com> wrote:
> On CPUs that support S2FWB (Armv8.4+), KVM configures the stage 2 page
> tables to override the memory attributes of memory accesses, regardless
> of the stage 1 page table configurations, and also when the stage 1 MMU
> is turned off.  This results in all memory accesses to RAM being
> cacheable, including during early boot of the guest.
> On CPUs without this feature, memory accesses were non-cacheable during
> boot until the guest turned on the stage 1 MMU, and we had to detect
> when the guest turned on the MMU, such that we could invalidate all cache
> entries and ensure a consistent view of memory with the MMU turned on.
> When the guest turned on the caches, we would call stage2_flush_vm()
> from kvm_toggle_cache().
> However, stage2_flush_vm() walks all the stage 2 tables, and calls
> __kvm_flush-dcache_pte, which on a system with S2FWD does ... absolutely


> nothing.
> We can avoid that whole song and dance, and simply not set TVM when
> creating a VM on a system that has S2FWB.
> Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>

Apart from the nit above, and Mark's other remark, it looks good to
me. I'll fix them up when applying the patch.



Jazz is not dead, it just smells funny.
kvmarm mailing list

  parent reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-28 13:05 Christoffer Dall
2019-10-28 13:28 ` Mark Rutland
2019-10-28 13:45 ` Marc Zyngier [this message]
2019-10-28 15:06 ` Alexandru Elisei
2019-10-28 15:12 ` Alexandru Elisei
2019-10-28 16:19   ` Marc Zyngier
2019-10-28 17:09     ` Mark Rutland
2019-11-06 13:02 ` Alexandru Elisei
2019-11-06 15:20   ` Christoffer Dall

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