From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: kvm@vger.kernel.org, x86@kernel.org,
Paolo Bonzini <pbonzini@redhat.com>,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
Wanpeng Li <wanpengli@tencent.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Jim Mattson <jmattson@google.com>, Gavin Shan <gshan@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/8] KVM: x86: Interrupt-based mechanism for async_pf 'page present' notifications
Date: Thu, 14 May 2020 20:14:31 +0200 [thread overview]
Message-ID: <87lfluwfi0.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20200513141644.GD173965@redhat.com>
Vivek Goyal <vgoyal@redhat.com> writes:
> On Mon, May 11, 2020 at 06:47:44PM +0200, Vitaly Kuznetsov wrote:
>> Concerns were expressed around (ab)using #PF for KVM's async_pf mechanism,
>> it seems that re-using #PF exception for a PV mechanism wasn't a great
>> idea after all. The Grand Plan is to switch to using e.g. #VE for 'page
>> not present' events and normal APIC interrupts for 'page ready' events.
>> This series does the later.
>
> Hi Vitaly,
>
> How does any of this impact nested virtualization code (if any).
>
> I have tried understanding that logic, but I have to admit, I could
> never get it.
>
> arch/x86/kvm/mmu/mmu.c
>
> int kvm_handle_page_fault(struct kvm_vcpu *vcpu, u64 error_code,
> u64 fault_address, char *insn, int insn_len)
> {
> switch (vcpu->arch.apf.host_apf_reason) {
> case KVM_PV_REASON_PAGE_NOT_PRESENT:
> kvm_async_pf_task_wait(fault_address, 0);
> case KVM_PV_REASON_PAGE_READY:
> kvm_async_pf_task_wake(fault_address);
> }
> }
>
"[PATCH 8/8] KVM: x86: drop KVM_PV_REASON_PAGE_READY case from
kvm_handle_page_fault()" modifies this a little bit.
Basically (and if I understand this correctly) we have the following APF
related feature (bit 2 in MSR_KVM_ASYNC_PF_EN): "asynchronous page faults
are delivered to L1 as #PF vmexits.". When enabled, it allows L0 to
inject #PF when L2 guest is running. L1 will see this as '#PF vmexit'
and the code you cite will do exactly what do_async_page_fault() is
doing.
When we switch to interrupt based delivery for 'page ready' events we
don't need a special handling for them in L1 (as we don't need any
special handling for all interrupts from devices in kernel when KVM
guest is running).
I have to admit I haven't tested nested scenario yet, "what could go
wrong?" :-)
--
Vitaly
prev parent reply other threads:[~2020-05-14 18:14 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-11 16:47 [PATCH 0/8] KVM: x86: Interrupt-based mechanism for async_pf 'page present' notifications Vitaly Kuznetsov
2020-05-11 16:47 ` [PATCH 1/8] Revert "KVM: async_pf: Fix #DF due to inject "Page not Present" and "Page Ready" exceptions simultaneously" Vitaly Kuznetsov
2020-05-11 16:47 ` [PATCH 2/8] KVM: x86: extend struct kvm_vcpu_pv_apf_data with token info Vitaly Kuznetsov
2020-05-12 15:27 ` Vivek Goyal
2020-05-12 15:40 ` Vitaly Kuznetsov
2020-05-12 15:53 ` Vivek Goyal
2020-05-12 17:50 ` Sean Christopherson
2020-05-13 9:09 ` Vitaly Kuznetsov
2020-05-13 12:52 ` Vivek Goyal
2020-05-15 15:59 ` Paolo Bonzini
2020-05-15 18:46 ` Sean Christopherson
2020-05-15 19:18 ` Paolo Bonzini
2020-05-15 20:33 ` Vivek Goyal
2020-05-15 20:53 ` Sean Christopherson
2020-05-15 20:43 ` Sean Christopherson
2020-05-15 22:23 ` Paolo Bonzini
2020-05-15 23:16 ` Sean Christopherson
2020-05-21 14:59 ` Vitaly Kuznetsov
2020-05-22 7:33 ` Paolo Bonzini
2020-05-12 21:15 ` Vivek Goyal
2020-05-21 18:38 ` Vivek Goyal
2020-05-23 16:34 ` Vitaly Kuznetsov
2020-05-26 12:50 ` Vivek Goyal
2020-05-11 16:47 ` [PATCH 3/8] KVM: introduce kvm_read_guest_offset_cached() Vitaly Kuznetsov
2020-05-11 16:47 ` [PATCH 4/8] KVM: x86: interrupt based APF page-ready event delivery Vitaly Kuznetsov
2020-05-12 14:24 ` Vivek Goyal
2020-05-12 15:50 ` Vitaly Kuznetsov
2020-05-12 18:07 ` Vivek Goyal
2020-05-13 9:03 ` Vitaly Kuznetsov
2020-05-13 13:53 ` Vivek Goyal
2020-05-13 14:03 ` Vivek Goyal
2020-05-13 14:23 ` Vitaly Kuznetsov
2020-05-13 18:46 ` Vivek Goyal
2020-05-14 8:08 ` Vitaly Kuznetsov
2020-05-14 13:31 ` Vivek Goyal
2020-05-11 16:47 ` [PATCH 5/8] KVM: x86: acknowledgment mechanism for async pf page ready notifications Vitaly Kuznetsov
2020-05-11 16:47 ` [PATCH 6/8] KVM: x86: announce KVM_FEATURE_ASYNC_PF_INT Vitaly Kuznetsov
2020-05-11 16:47 ` [PATCH 7/8] KVM: x86: Switch KVM guest to using interrupts for page ready APF delivery Vitaly Kuznetsov
2020-05-13 1:44 ` [kbuild-all] " kbuild test robot
2020-05-11 16:47 ` [PATCH 8/8] KVM: x86: drop KVM_PV_REASON_PAGE_READY case from kvm_handle_page_fault() Vitaly Kuznetsov
2020-05-12 15:32 ` [PATCH 0/8] KVM: x86: Interrupt-based mechanism for async_pf 'page present' notifications Vivek Goyal
2020-05-12 16:12 ` Vitaly Kuznetsov
2020-05-13 14:16 ` Vivek Goyal
2020-05-14 18:14 ` Vitaly Kuznetsov [this message]
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