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From: Marc Zyngier <maz@kernel.org>
To: Gavin Shan <gshan@redhat.com>
Cc: catalin.marinas@arm.com, linux-kernel@vger.kernel.org,
	shan.gavin@gmail.com, Paolo Bonzini <pbonzini@redhat.com>,
	will@kernel.org, kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH RFCv2 9/9] arm64: Support async page fault
Date: Fri, 29 May 2020 10:41:44 +0100	[thread overview]
Message-ID: <6965aaf641a23fab64fbe2ceeb790272@kernel.org> (raw)
In-Reply-To: <6a4a82a4-af01-98c2-c854-9199f55f7bd3@redhat.com>

On 2020-05-29 00:02, Gavin Shan wrote:
> Hi Paolo,
> 
> On 5/28/20 8:48 PM, Paolo Bonzini wrote:
>> On 28/05/20 08:14, Gavin Shan wrote:
>>>> - for x86 we're also thinking of initiating the page fault from the
>>>> exception handler, rather than doing so from the hypervisor before
>>>> injecting the exception.  If ARM leads the way here, we would do our
>>>> best to share code when x86 does the same.
>>> 
>>> Sorry, Paolo, I don't follow your idea here. Could you please provide
>>> more details?
>> 
>> The idea is to inject stage2 page faults into the guest even before 
>> the
>> host starts populates the page.  The guest then invokes a hypercall,
>> telling the host to populate the page table and inject the 'page 
>> ready'
>> event (interrupt) when it's done.
>> 
>> 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.
> 
> 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.

         M.
-- 
Jazz is not dead. It just smells funny...
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  reply	other threads:[~2020-05-29  9:41 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 [this message]
2020-05-29 11:11             ` Paolo Bonzini
2020-05-31 12:44               ` Marc Zyngier
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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