Re: [PATCH v2 08/10] KVM: x86: Switch KVM guest to using interrupts for page ready APF delivery
From: Vivek Goyal
Date: Wed Jun 10 2020 - 16:51:55 EST
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 <vkuznets@xxxxxxxxxx>
> ---
> 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
>