Re: [RFC v3 2/5] KVM: x86: add support for ioregionfd signal handling

Jason Wang
2021-03-09T05:52:40Z

On 2021/2/21 8:04 下午, Elena Afanasova wrote:
> The vCPU thread may receive a signal during ioregionfd communication,
> ioctl(KVM_RUN) needs to return to userspace and then ioctl(KVM_RUN)
> must resume ioregionfd.

After a glance at the patch, I wonder can we split the patch into two?

1) sleepable iodevice which is not supported currently, probably with a
new cap?
2) ioregionfd specific codes (I wonder if it has any)

Then the sleepable iodevice could be reused by future features.

>
> Signed-off-by: Elena Afanasova <eafanasova@gmail.com>
> ---
> v3:
> - add FAST_MMIO bus support
> - move ioregion_interrupted flag to ioregion_ctx
> - reorder ioregion_ctx fields
> - rework complete_ioregion operations
> - add signal handling support for crossing a page boundary case
> - fix kvm_arch_vcpu_ioctl_run() should return -EINTR in case ioregionfd
> is interrupted
>
> arch/x86/kvm/vmx/vmx.c | 40 +++++-
> arch/x86/kvm/x86.c | 272 +++++++++++++++++++++++++++++++++++++--
> include/linux/kvm_host.h | 10 ++
> virt/kvm/kvm_main.c | 16 ++-
> 4 files changed, 317 insertions(+), 21 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 47b8357b9751..39db31afd27e 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5357,19 +5357,51 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
> return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0);
> }
>
> +#ifdef CONFIG_KVM_IOREGION
> +static int complete_ioregion_fast_mmio(struct kvm_vcpu *vcpu)
> +{
> + int ret, idx;
> +
> + idx = srcu_read_lock(&vcpu->kvm->srcu);
> + ret = kvm_io_bus_write(vcpu, KVM_FAST_MMIO_BUS,
> + vcpu->ioregion_ctx.addr, 0, NULL);
> + if (ret) {
> + ret = kvm_mmu_page_fault(vcpu, vcpu->ioregion_ctx.addr,
> + PFERR_RSVD_MASK, NULL, 0);
> + srcu_read_unlock(&vcpu->kvm->srcu, idx);
> + return ret;
> + }
> +
> + srcu_read_unlock(&vcpu->kvm->srcu, idx);
> + return kvm_skip_emulated_instruction(vcpu);
> +}
> +#endif
> +
> static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
> {
> gpa_t gpa;
> + int ret;
>
> /*
> * A nested guest cannot optimize MMIO vmexits, because we have an
> * nGPA here instead of the required GPA.
> */
> gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
> - if (!is_guest_mode(vcpu) &&
> - !kvm_io_bus_write(vcpu, KVM_FAST_MMIO_BUS, gpa, 0, NULL)) {
> - trace_kvm_fast_mmio(gpa);
> - return kvm_skip_emulated_instruction(vcpu);
> + if (!is_guest_mode(vcpu)) {
> + ret = kvm_io_bus_write(vcpu, KVM_FAST_MMIO_BUS, gpa, 0, NULL);
> + if (!ret) {
> + trace_kvm_fast_mmio(gpa);
> + return kvm_skip_emulated_instruction(vcpu);
> + }
> +
> +#ifdef CONFIG_KVM_IOREGION
> + if (unlikely(vcpu->ioregion_ctx.is_interrupted && ret == -EINTR)) {

So the question still, EINTR looks wrong which means the syscall can't
be restarted. Not that the syscal doesn't mean KVM_RUN but actually the
kernel_read|write() you want to do with the ioregion fd.

Also do we need to treat differently for EINTR and ERESTARTSYS since
EINTR means the kernel_read()|write() can't be resumed.

Thanks