From: Marc Zyngier <maz@kernel.org>
To: Will Deacon <will@kernel.org>
Cc: kvm@vger.kernel.org, kernel-team@android.com,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH] KVM: arm64: Cap default IPA size to the host's own size
Date: Tue, 09 Mar 2021 11:35:54 +0000 [thread overview]
Message-ID: <87o8fsy2xx.wl-maz@kernel.org> (raw)
In-Reply-To: <20210309112658.GA28025@willie-the-truck>
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).
M.
--
Without deviation from the norm, progress is not possible.
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Will Deacon <will@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, 09 Mar 2021 11:35:54 +0000 [thread overview]
Message-ID: <87o8fsy2xx.wl-maz@kernel.org> (raw)
In-Reply-To: <20210309112658.GA28025@willie-the-truck>
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).
M.
--
Without deviation from the norm, progress is not possible.
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Will Deacon <will@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, 09 Mar 2021 11:35:54 +0000 [thread overview]
Message-ID: <87o8fsy2xx.wl-maz@kernel.org> (raw)
In-Reply-To: <20210309112658.GA28025@willie-the-truck>
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).
M.
--
Without deviation from the norm, progress is not possible.
next prev parent reply other threads:[~2021-03-09 11:36 UTC|newest]
Thread overview: 30+ 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
2021-03-08 17:46 ` Marc Zyngier
2021-03-08 17:46 ` Marc Zyngier
2021-03-09 11:09 ` Suzuki Poulose
2021-03-09 11:09 ` Suzuki Poulose
2021-03-09 11:09 ` Suzuki Poulose
2021-03-09 14:25 ` Marc Zyngier
2021-03-09 14:25 ` Marc Zyngier
2021-03-09 14:25 ` Marc Zyngier
2021-03-09 11:26 ` Will Deacon
2021-03-09 11:26 ` Will Deacon
2021-03-09 11:26 ` Will Deacon
2021-03-09 11:35 ` Marc Zyngier [this message]
2021-03-09 11:35 ` Marc Zyngier
2021-03-09 11:35 ` Marc Zyngier
2021-03-09 11:40 ` Will Deacon
2021-03-09 11:40 ` Will Deacon
2021-03-09 11:40 ` Will Deacon
2021-03-09 13:20 ` Andrew Jones
2021-03-09 13:20 ` Andrew Jones
2021-03-09 13:20 ` Andrew Jones
2021-03-09 13:43 ` Marc Zyngier
2021-03-09 13:43 ` Marc Zyngier
2021-03-09 13:43 ` Marc Zyngier
2021-03-09 14:29 ` Andrew Jones
2021-03-09 14:29 ` Andrew Jones
2021-03-09 14:29 ` Andrew Jones
2021-03-09 14:46 ` Marc Zyngier
2021-03-09 14:46 ` Marc Zyngier
2021-03-09 14:46 ` Marc Zyngier
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