Re: [PATCH 0/8] KVM: x86: Interrupt-based mechanism for async_pf 'page present' notifications

Vivek Goyal
2020-05-13T14:16:54Z

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
>