From: Paolo Bonzini <pbonzini@redhat.com>
To: James Morse <james.morse@arm.com>, Gavin Shan <gshan@redhat.com>,
kvmarm@lists.cs.columbia.edu
Cc: maz@kernel.org, will@kernel.org, shan.gavin@gmail.com
Subject: Re: [PATCH 0/6] Support Asynchronous Page Fault
Date: Sat, 31 Oct 2020 15:18:26 +0100 [thread overview]
Message-ID: <ae863cb3-4faf-555d-c34d-04b97d3ef486@redhat.com> (raw)
In-Reply-To: <4dcaea7a-a4d1-9bf3-eb95-ea9d8826ad99@arm.com>
On 23/10/20 18:54, James Morse wrote:
> SDEI gives you an NMI ... which you use to set a TIF flag. This can only work reliably for
> user-space. So much so that you have code in the hypervisor to only deliver the NMI ...
> when in user-space.
> The only reason you would need an NMI is to interrupt interrupts-masked code. Linux can't
> reschedule when this is the case.
>
> I can only conclude, you really don't need an NMI here.
I don't think the issue is that you want an NMI. It is just that the
synchronous interruption that we want is exactly the same as a SDEI, and
so is the notification reply from the guest to the host (e.g. accept the
async pagefault or process it synchronously).
Yes, it's more code, but at least in x86 world we tried hard not to
invent new paravirtualized mechanisms if we could avoid it, especially
in the host->guest direction, and it's almost always paid off. This is
because in case we don't get things right, it's much much harder to fix
them on both the hypervisor and the guest side; by relying on existing
code that work on bare metal hardware, the guest side exists already and
you can develop against it.
Paolo
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next prev parent reply other threads:[~2020-10-31 14:18 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-18 1:13 [PATCH 0/6] Support Asynchronous Page Fault Gavin Shan
2020-08-18 1:13 ` [PATCH 1/6] arm64: Probe for the presence of KVM hypervisor services during boot Gavin Shan
2020-08-18 1:13 ` [PATCH 2/6] arm/arm64: KVM: Advertise KVM UID to guests via SMCCC Gavin Shan
2020-08-18 1:13 ` [PATCH 3/6] kvm/arm64: Export kvm_handle_user_mem_abort() with prefault mode Gavin Shan
2020-10-23 16:54 ` James Morse
2020-11-02 5:30 ` Gavin Shan
2020-08-18 1:13 ` [PATCH 4/6] arm64/kvm: Support async page fault Gavin Shan
2020-10-23 17:01 ` James Morse
2020-11-02 7:19 ` Gavin Shan
2020-08-18 1:13 ` [PATCH 5/6] drivers/acpi: Import ACPI APF table Gavin Shan
2020-10-23 16:55 ` James Morse
2020-08-18 1:13 ` [PATCH 6/6] arm64/kernel: Support async page fault Gavin Shan
2020-10-23 16:54 ` [PATCH 0/6] Support Asynchronous Page Fault James Morse
2020-10-31 14:18 ` Paolo Bonzini [this message]
2020-11-02 5:23 ` Gavin Shan
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