From: Will Deacon <will@kernel.org>
To: Marc Zyngier <maz@kernel.org>
Cc: kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
kernel-team@android.com
Subject: Re: [PATCH] KVM: arm64: Cap default IPA size to the host's own size
Date: Tue, 9 Mar 2021 11:40:32 +0000 [thread overview]
Message-ID: <20210309114031.GA28091@willie-the-truck> (raw)
In-Reply-To: <87o8fsy2xx.wl-maz@kernel.org>
On Tue, Mar 09, 2021 at 11:35:54AM +0000, Marc Zyngier wrote:
> On Tue, 09 Mar 2021 11:26:59 +0000,
> Will Deacon <will@kernel.org> wrote:
> >
> > On Mon, Mar 08, 2021 at 05:46:43PM +0000, Marc Zyngier wrote:
> > > KVM/arm64 has forever used a 40bit default IPA space, partially
> > > due to its 32bit heritage (where the only choice is 40bit).
> > >
> > > However, there are implementations in the wild that have a *cough*
> > > much smaller *cough* IPA space, which leads to a misprogramming of
> > > VTCR_EL2, and a guest that is stuck on its first memory access
> > > if userspace dares to ask for the default IPA setting (which most
> > > VMMs do).
> > >
> > > Instead, cap the default IPA size to what the host can actually
> > > do, and spit out a one-off message on the console. The boot warning
> > > is turned into a more meaningfull message, and the new behaviour
> > > is also documented.
> > >
> > > Although this is a userspace ABI change, it doesn't really change
> > > much for userspace:
> > >
> > > - the guest couldn't run before this change, while it now has
> > > a chance to if the memory range fits the reduced IPA space
> > >
> > > - a memory slot that was accepted because it did fit the default
> > > IPA space but didn't fit the HW constraints is now properly
> > > rejected
> > >
> > > The other thing that's left doing is to convince userspace to
> > > actually use the IPA space setting instead of relying on the
> > > antiquated default.
> >
> > Is there a way for userspace to discover the default IPA size, or does
> > it have to try setting values until it finds one that sticks?
>
> Yes, since 233a7cb23531 ("kvm: arm64: Allow tuning the physical
> address size for VM").
>
> The VMM can issue a KVM_CAP_ARM_VM_IPA_SIZE ioctl(), and get in return
> the maximum IPA size (I have a patch for kvmtool that does this).
Great, thanks -- that's exactly what I was thinking about when I asked the
question!
Will
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next prev parent reply other threads:[~2021-03-09 11:42 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-08 17:46 [PATCH] KVM: arm64: Cap default IPA size to the host's own size Marc Zyngier
2021-03-09 11:09 ` Suzuki Poulose
2021-03-09 14:25 ` Marc Zyngier
2021-03-09 11:26 ` Will Deacon
2021-03-09 11:35 ` Marc Zyngier
2021-03-09 11:40 ` Will Deacon [this message]
2021-03-09 13:20 ` Andrew Jones
2021-03-09 13:43 ` Marc Zyngier
2021-03-09 14:29 ` Andrew Jones
2021-03-09 14:46 ` Marc Zyngier
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