On Mon, May 25, 2020 at 04:41:23PM +0200, Vitaly Kuznetsov wrote:
> KVM now supports using interrupt for 'page ready' APF event delivery and
> legacy mechanism was deprecated. Switch KVM guests to the new one.

Hi Vitaly,

I see we have all this code in guest which tries to take care of
cases where PAGE_READY can be delivered before PAGE_NOT_PRESENT. In
this new schedume of things, can it still happen. We are using
an exception to deliver PAGE_NOT_PRESENT while using interrupt to
deliver PAGE_READY.

If re-ordeing is not possible, then it will be good to get rid of
that extra complexity in guest.

Thanks
Vivek

> 
> Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
> ---
>  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_para.h    |  6 ++++
>  arch/x86/kernel/irq.c              |  9 ++++++
>  arch/x86/kernel/kvm.c              | 45 ++++++++++++++++++++++--------
>  7 files changed, 66 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
> index b67bae7091d7..d574dadcb2a1 100644
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -1475,6 +1475,11 @@ BUILD_INTERRUPT3(hv_stimer0_callback_vector, 
> HYPERV_STIMER0_VECTOR,
>  
>  #endif /* CONFIG_HYPERV */
>  
> +#ifdef CONFIG_KVM_GUEST
> +BUILD_INTERRUPT3(kvm_async_pf_vector, KVM_ASYNC_PF_VECTOR,
> +              kvm_async_pf_intr)
> +#endif
> +
>  SYM_CODE_START(page_fault)
>       ASM_CLAC
>       pushl   $do_page_fault
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 3063aa9090f9..138f5c5aca2e 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -1190,6 +1190,11 @@ apicinterrupt3 HYPERVISOR_CALLBACK_VECTOR \
>       acrn_hv_callback_vector acrn_hv_vector_handler
>  #endif
>  
> +#ifdef CONFIG_KVM_GUEST
> +apicinterrupt3 KVM_ASYNC_PF_VECTOR \
> +     kvm_async_pf_vector kvm_async_pf_intr
> +#endif
> +
>  idtentry debug                       do_debug                
> has_error_code=0        paranoid=1 shift_ist=IST_INDEX_DB 
> ist_offset=DB_STACK_OFFSET
>  idtentry int3                        do_int3                 
> has_error_code=0        create_gap=1
>  idtentry stack_segment               do_stack_segment        has_error_code=1
> diff --git a/arch/x86/include/asm/hardirq.h b/arch/x86/include/asm/hardirq.h
> index 07533795b8d2..be0fbb15ad7f 100644
> --- a/arch/x86/include/asm/hardirq.h
> +++ b/arch/x86/include/asm/hardirq.h
> @@ -44,6 +44,9 @@ typedef struct {
>       unsigned int irq_hv_reenlightenment_count;
>       unsigned int hyperv_stimer0_count;
>  #endif
> +#ifdef CONFIG_KVM_GUEST
> +     unsigned int kvm_async_pf_pageready_count;
> +#endif
>  } ____cacheline_aligned irq_cpustat_t;
>  
>  DECLARE_PER_CPU_SHARED_ALIGNED(irq_cpustat_t, irq_stat);
> diff --git a/arch/x86/include/asm/irq_vectors.h 
> b/arch/x86/include/asm/irq_vectors.h
> index 889f8b1b5b7f..8879a9ecd908 100644
> --- a/arch/x86/include/asm/irq_vectors.h
> +++ b/arch/x86/include/asm/irq_vectors.h
> @@ -104,7 +104,11 @@
>  #define HYPERV_STIMER0_VECTOR                0xed
>  #endif
>  
> -#define LOCAL_TIMER_VECTOR           0xec
> +#ifdef CONFIG_KVM_GUEST
> +#define KVM_ASYNC_PF_VECTOR          0xec
> +#endif
> +
> +#define LOCAL_TIMER_VECTOR           0xeb
>  
>  #define NR_VECTORS                    256
>  
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index 2a3102fee189..a075cd8fa5c7 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -4,6 +4,7 @@
>  
>  #include <asm/processor.h>
>  #include <asm/alternative.h>
> +#include <linux/interrupt.h>
>  #include <uapi/asm/kvm_para.h>
>  
>  extern void kvmclock_init(void);
> @@ -93,6 +94,11 @@ void kvm_async_pf_task_wake(u32 token);
>  u32 kvm_read_and_reset_apf_flags(void);
>  extern void kvm_disable_steal_time(void);
>  void do_async_page_fault(struct pt_regs *regs, unsigned long error_code, 
> unsigned long address);
> +extern __visible void kvm_async_pf_vector(void);
> +#ifdef CONFIG_TRACING
> +#define trace_kvm_async_pf_vector kvm_async_pf_vector
> +#endif
> +__visible void __irq_entry kvm_async_pf_intr(struct pt_regs *regs);
>  
>  #ifdef CONFIG_PARAVIRT_SPINLOCKS
>  void __init kvm_spinlock_init(void);
> diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
> index c7965ff429c5..a4c2f25ad74d 100644
> --- a/arch/x86/kernel/irq.c
> +++ b/arch/x86/kernel/irq.c
> @@ -159,6 +159,15 @@ int arch_show_interrupts(struct seq_file *p, int prec)
>                                  irq_stats(j)->hyperv_stimer0_count);
>               seq_puts(p, "  Hyper-V stimer0 interrupts\n");
>       }
> +#endif
> +#ifdef CONFIG_KVM_GUEST
> +     if (test_bit(KVM_ASYNC_PF_VECTOR, system_vectors)) {
> +             seq_printf(p, "%*s: ", prec, "APF");
> +             for_each_online_cpu(j)
> +                     seq_printf(p, "%10u ",
> +                                irq_stats(j)->kvm_async_pf_pageready_count);
> +             seq_puts(p, "  KVM async PF page ready interrupts\n");
> +     }
>  #endif
>       seq_printf(p, "%*s: %10u\n", prec, "ERR", atomic_read(&irq_err_count));
>  #if defined(CONFIG_X86_IO_APIC)
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 340df5dab30d..79730eaef1e1 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -245,23 +245,39 @@ NOKPROBE_SYMBOL(kvm_read_and_reset_apf_flags);
>  dotraplinkage void
>  do_async_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned 
> long address)
>  {
> -     switch (kvm_read_and_reset_apf_flags()) {
> -     default:
> +     u32 flags = kvm_read_and_reset_apf_flags();
> +
> +     if (!flags) {
> +             /* This is a normal page fault */
>               do_page_fault(regs, error_code, address);
> -             break;
> -     case KVM_PV_REASON_PAGE_NOT_PRESENT:
> +             return;
> +     } else if (flags & KVM_PV_REASON_PAGE_NOT_PRESENT) {
>               /* page is swapped out by the host. */
>               kvm_async_pf_task_wait((u32)address, !user_mode(regs));
> -             break;
> -     case KVM_PV_REASON_PAGE_READY:
> -             rcu_irq_enter();
> -             kvm_async_pf_task_wake((u32)address);
> -             rcu_irq_exit();
> -             break;
> +     } else {
> +             WARN_ONCE(1, "Unexpected async PF flags: %x\n", flags);
>       }
>  }
>  NOKPROBE_SYMBOL(do_async_page_fault);
>  
> +__visible void __irq_entry kvm_async_pf_intr(struct pt_regs *regs)
> +{
> +     u32 token;
> +
> +     entering_ack_irq();
> +
> +     inc_irq_stat(kvm_async_pf_pageready_count);
> +
> +     if (__this_cpu_read(apf_reason.enabled)) {
> +             token = __this_cpu_read(apf_reason.token);
> +             kvm_async_pf_task_wake(token);
> +             __this_cpu_write(apf_reason.token, 0);
> +             wrmsrl(MSR_KVM_ASYNC_PF_ACK, 1);
> +     }
> +
> +     exiting_irq();
> +}
> +
>  static void __init paravirt_ops_setup(void)
>  {
>       pv_info.name = "KVM";
> @@ -305,17 +321,19 @@ static notrace void kvm_guest_apic_eoi_write(u32 reg, 
> u32 val)
>  
>  static void kvm_guest_cpu_init(void)
>  {
> -     if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF) && kvmapf) {
> +     if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF_INT) && kvmapf) {
>               u64 pa = slow_virt_to_phys(this_cpu_ptr(&apf_reason));
>  
>  #ifdef CONFIG_PREEMPTION
>               pa |= KVM_ASYNC_PF_SEND_ALWAYS;
>  #endif
> -             pa |= KVM_ASYNC_PF_ENABLED;
> +             pa |= KVM_ASYNC_PF_ENABLED | KVM_ASYNC_PF_DELIVERY_AS_INT;
>  
>               if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF_VMEXIT))
>                       pa |= KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT;
>  
> +             wrmsrl(MSR_KVM_ASYNC_PF_INT, KVM_ASYNC_PF_VECTOR);
> +
>               wrmsrl(MSR_KVM_ASYNC_PF_EN, pa);
>               __this_cpu_write(apf_reason.enabled, 1);
>               printk(KERN_INFO"KVM setup async PF for cpu %d\n",
> @@ -649,6 +667,9 @@ static void __init kvm_guest_init(void)
>       if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
>               apic_set_eoi_write(kvm_guest_apic_eoi_write);
>  
> +     if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF_INT))
> +             alloc_intr_gate(KVM_ASYNC_PF_VECTOR, kvm_async_pf_vector);
> +
>  #ifdef CONFIG_SMP
>       smp_ops.smp_prepare_cpus = kvm_smp_prepare_cpus;
>       smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
> -- 
> 2.25.4
> 

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