From: Marc Zyngier <maz@kernel.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gavin Shan <gshan@redhat.com>,
kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
shan.gavin@gmail.com, catalin.marinas@arm.com, will@kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH RFCv2 9/9] arm64: Support async page fault
Date: Sun, 31 May 2020 13:44:40 +0100 [thread overview]
Message-ID: <4337cca152df47c93d96e092189a0e36@kernel.org> (raw)
In-Reply-To: <d0bfb944-b50a-608a-7dcc-5a409cdc4524@redhat.com>
On 2020-05-29 12:11, Paolo Bonzini wrote:
> On 29/05/20 11:41, Marc Zyngier wrote:
>>>>
>>>>
>>>> For x86 the advantage is that the processor can take care of raising
>>>> the
>>>> stage2 page fault in the guest, so it's faster.
>>>>
>>> I think there might be too much overhead if the page can be populated
>>> quickly by host. For example, it's fast to populate the pages if
>>> swapin
>>> isn't involved.
>
> Those would still be handled by the host. Only those that are not
> present in the host (which you can see through the MMU notifier) would
> be routed to the guest. You can do things differently between "not
> present fault because the page table does not exist" and "not present
> fault because the page is missing in the host".
>
>>> If I'm correct enough, it seems arm64 doesn't have similar mechanism,
>>> routing stage2 page fault to guest.
>>
>> Indeed, this isn't a thing on arm64. Exception caused by a S2 fault
>> are
>> always routed to EL2.
>
> Is there an ARM-approved way to reuse the S2 fault syndromes to detect
> async page faults?
It would mean being able to set an ESR_EL2 register value into ESR_EL1,
and there is nothing in the architecture that would allow that, with
the exception of nested virt: a VHE guest hypervisor running at EL1
must be able to observe S2 faults for its own S2, as synthesized by
the host hypervisor.
The trouble is that:
- there is so far no commercially available CPU supporting NV
- even if you could get hold of such a machine, there is no
guarantee that such "EL2 syndrome at EL1" is valid outside of
the nested context
- this doesn't solve the issue for non-NV CPUs anyway
> (By the way, another "modern" use for async page faults is for postcopy
> live migration).
Right. That's definitely a more interesting version of "swap-in".
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2020-05-31 12:44 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-08 3:29 [PATCH RFCv2 0/9] kvm/arm64: Support Async Page Fault Gavin Shan
2020-05-08 3:29 ` [PATCH RFCv2 1/9] arm64: Probe for the presence of KVM hypervisor services during boot Gavin Shan
2020-05-08 3:29 ` [PATCH RFCv2 2/9] arm/arm64: KVM: Advertise KVM UID to guests via SMCCC Gavin Shan
2020-05-08 3:29 ` [PATCH RFCv2 3/9] kvm/arm64: Rename kvm_vcpu_get_hsr() to kvm_vcpu_get_esr() Gavin Shan
2020-05-26 10:42 ` Mark Rutland
2020-05-27 2:43 ` Gavin Shan
2020-05-27 7:20 ` Marc Zyngier
2020-05-28 6:34 ` Gavin Shan
2020-05-08 3:29 ` [PATCH RFCv2 4/9] kvm/arm64: Detach ESR operator from vCPU struct Gavin Shan
2020-05-26 10:51 ` Mark Rutland
2020-05-27 2:55 ` Gavin Shan
2020-05-08 3:29 ` [PATCH RFCv2 5/9] kvm/arm64: Replace hsr with esr Gavin Shan
2020-05-26 10:45 ` Mark Rutland
2020-05-27 2:56 ` Gavin Shan
2020-05-08 3:29 ` [PATCH RFCv2 6/9] kvm/arm64: Export kvm_handle_user_mem_abort() with prefault mode Gavin Shan
2020-05-26 10:58 ` Mark Rutland
2020-05-27 3:01 ` Gavin Shan
2020-05-08 3:29 ` [PATCH RFCv2 7/9] kvm/arm64: Support async page fault Gavin Shan
2020-05-26 12:34 ` Mark Rutland
2020-05-27 4:05 ` Gavin Shan
2020-05-27 7:37 ` Marc Zyngier
2020-05-28 6:32 ` Gavin Shan
2020-05-08 3:29 ` [PATCH RFCv2 8/9] kernel/sched: Add cpu_rq_is_locked() Gavin Shan
2020-05-08 3:29 ` [PATCH RFCv2 9/9] arm64: Support async page fault Gavin Shan
2020-05-26 12:56 ` Mark Rutland
2020-05-27 6:48 ` Paolo Bonzini
2020-05-28 6:14 ` Gavin Shan
2020-05-28 7:03 ` Marc Zyngier
2020-05-28 10:53 ` Paolo Bonzini
2020-05-28 10:48 ` Paolo Bonzini
2020-05-28 23:02 ` Gavin Shan
2020-05-29 9:41 ` Marc Zyngier
2020-05-29 11:11 ` Paolo Bonzini
2020-05-31 12:44 ` Marc Zyngier [this message]
2020-06-01 9:21 ` Paolo Bonzini
2020-06-02 5:44 ` Gavin Shan
2020-05-25 23:39 ` [PATCH RFCv2 0/9] kvm/arm64: Support Async Page Fault Gavin Shan
2020-05-26 13:09 ` Mark Rutland
2020-05-27 2:39 ` Gavin Shan
2020-05-27 7:48 ` Marc Zyngier
2020-05-27 16:10 ` Paolo Bonzini
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