linux-kernel - Re: [PATCH 0/8] KVM: x86: Interrupt-based mechanism for async

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200513141644.GD173965@redhat.com>
Date:   Wed, 13 May 2020 10:16:44 -0400
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        Gavin Shan <gshan@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/8] KVM: x86: Interrupt-based mechanism for async_pf
 'page present' notifications

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);
	}
}

Vivek

> 
> Changes since RFC:
> - Using #PF for 'page ready' is deprecated and removed [Paolo Bonzini]
> - 'reason' field in 'struct kvm_vcpu_pv_apf_data' is not used for 'page ready'
>   notifications and 'pageready_token' is not used for 'page not present' events
>   [Paolo Bonzini]
> - Renamed MSR_KVM_ASYNC_PF2 -> MSR_KVM_ASYNC_PF_INT [Peter Xu]
> - Drop 'enabled' field from MSR_KVM_ASYNC_PF_INT [Peter Xu]
> - Other minor changes supporting the above.
> 
> Vitaly Kuznetsov (8):
>   Revert "KVM: async_pf: Fix #DF due to inject "Page not Present" and
>     "Page Ready" exceptions simultaneously"
>   KVM: x86: extend struct kvm_vcpu_pv_apf_data with token info
>   KVM: introduce kvm_read_guest_offset_cached()
>   KVM: x86: interrupt based APF page-ready event delivery
>   KVM: x86: acknowledgment mechanism for async pf page ready
>     notifications
>   KVM: x86: announce KVM_FEATURE_ASYNC_PF_INT
>   KVM: x86: Switch KVM guest to using interrupts for page ready APF
>     delivery
>   KVM: x86: drop KVM_PV_REASON_PAGE_READY case from
>     kvm_handle_page_fault()
> 
>  Documentation/virt/kvm/cpuid.rst     |   6 ++
>  Documentation/virt/kvm/msr.rst       | 106 ++++++++++++++------
>  arch/s390/include/asm/kvm_host.h     |   2 +
>  arch/x86/entry/entry_32.S            |   5 +
>  arch/x86/entry/entry_64.S            |   5 +
>  arch/x86/include/asm/hardirq.h       |   3 +
>  arch/x86/include/asm/irq_vectors.h   |   6 +-
>  arch/x86/include/asm/kvm_host.h      |   7 +-
>  arch/x86/include/asm/kvm_para.h      |   6 ++
>  arch/x86/include/uapi/asm/kvm_para.h |  11 ++-
>  arch/x86/kernel/irq.c                |   9 ++
>  arch/x86/kernel/kvm.c                |  42 ++++++--
>  arch/x86/kvm/cpuid.c                 |   3 +-
>  arch/x86/kvm/mmu/mmu.c               |  10 +-
>  arch/x86/kvm/x86.c                   | 142 ++++++++++++++++++---------
>  include/linux/kvm_host.h             |   3 +
>  include/uapi/linux/kvm.h             |   1 +
>  virt/kvm/async_pf.c                  |  10 ++
>  virt/kvm/kvm_main.c                  |  19 +++-
>  19 files changed, 295 insertions(+), 101 deletions(-)
> 
> -- 
> 2.25.4
>