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Date: Tue, 07 Jun 2022 12:33:33 +0300
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
Paolo Bonzini <pbonzini@...hat.com>
Cc: Sean Christopherson <seanjc@...gle.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Michael Kelley <mikelley@...rosoft.com>,
Siddharth Chandrasekaran <sidcha@...zon.de>,
Yuan Yao <yuan.yao@...ux.intel.com>,
linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 11/38] KVM: x86: hyper-v: Create a separate fifo for
L2 TLB flush
On Mon, 2022-06-06 at 10:36 +0200, Vitaly Kuznetsov wrote:
> To handle L2 TLB flush requests, KVM needs to use a separate fifo from
> regular (L1) Hyper-V TLB flush requests: e.g. when a request to flush
> something in L2 is made, the target vCPU can transition from L2 to L1,
> receive a request to flush a GVA for L1 and then try to enter L2 back.
> The first request needs to be processed at this point. Similarly,
> requests to flush GVAs in L1 must wait until L2 exits to L1.
>
> No functional change as KVM doesn't handle L2 TLB flush requests from
> L2 yet.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
> arch/x86/include/asm/kvm_host.h | 8 +++++++-
> arch/x86/kvm/hyperv.c | 11 +++++++----
> arch/x86/kvm/hyperv.h | 17 ++++++++++++++---
> 3 files changed, 28 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index cf3748be236d..0e58ab00dff0 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -613,6 +613,12 @@ struct kvm_vcpu_hv_synic {
> */
> #define KVM_HV_TLB_FLUSHALL_ENTRY ((u64)-1)
>
> +enum hv_tlb_flush_fifos {
> + HV_L1_TLB_FLUSH_FIFO,
> + HV_L2_TLB_FLUSH_FIFO,
> + HV_NR_TLB_FLUSH_FIFOS,
> +};
> +
> struct kvm_vcpu_hv_tlb_flush_fifo {
> spinlock_t write_lock;
> DECLARE_KFIFO(entries, u64, KVM_HV_TLB_FLUSH_FIFO_SIZE);
> @@ -638,7 +644,7 @@ struct kvm_vcpu_hv {
> u32 syndbg_cap_eax; /* HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES.EAX */
> } cpuid_cache;
>
> - struct kvm_vcpu_hv_tlb_flush_fifo tlb_flush_fifo;
> + struct kvm_vcpu_hv_tlb_flush_fifo tlb_flush_fifo[HV_NR_TLB_FLUSH_FIFOS];
> };
>
> /* Xen HVM per vcpu emulation context */
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index b347971b3924..32f223bbea6b 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -956,8 +956,10 @@ static int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)
>
> hv_vcpu->vp_index = vcpu->vcpu_idx;
>
> - INIT_KFIFO(hv_vcpu->tlb_flush_fifo.entries);
> - spin_lock_init(&hv_vcpu->tlb_flush_fifo.write_lock);
> + for (i = 0; i < HV_NR_TLB_FLUSH_FIFOS; i++) {
> + INIT_KFIFO(hv_vcpu->tlb_flush_fifo[i].entries);
> + spin_lock_init(&hv_vcpu->tlb_flush_fifo[i].write_lock);
> + }
>
> return 0;
> }
> @@ -1843,7 +1845,8 @@ static void hv_tlb_flush_enqueue(struct kvm_vcpu *vcpu, u64 *entries, int count)
> if (!hv_vcpu)
> return;
>
> - tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
> + /* kvm_hv_flush_tlb() is not ready to handle requests for L2s yet */
> + tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo[HV_L1_TLB_FLUSH_FIFO];
Yes, as expected here the local var starts to make sense.
>
> spin_lock_irqsave(&tlb_flush_fifo->write_lock, flags);
>
> @@ -1880,7 +1883,7 @@ void kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu)
> return;
> }
>
> - tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
> + tlb_flush_fifo = kvm_hv_get_tlb_flush_fifo(vcpu);
>
> count = kfifo_out(&tlb_flush_fifo->entries, entries, KVM_HV_TLB_FLUSH_FIFO_SIZE);
>
> diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
> index e5b32266ff7d..207d24efdc5a 100644
> --- a/arch/x86/kvm/hyperv.h
> +++ b/arch/x86/kvm/hyperv.h
> @@ -22,6 +22,7 @@
> #define __ARCH_X86_KVM_HYPERV_H__
>
> #include <linux/kvm_host.h>
> +#include "x86.h"
>
> /*
> * The #defines related to the synthetic debugger are required by KDNet, but
> @@ -147,16 +148,26 @@ int kvm_vm_ioctl_hv_eventfd(struct kvm *kvm, struct kvm_hyperv_eventfd *args);
> int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
> struct kvm_cpuid_entry2 __user *entries);
>
> +static inline struct kvm_vcpu_hv_tlb_flush_fifo *kvm_hv_get_tlb_flush_fifo(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> + int i = !is_guest_mode(vcpu) ? HV_L1_TLB_FLUSH_FIFO :
> + HV_L2_TLB_FLUSH_FIFO;
> +
> + /* KVM does not handle L2 TLB flush requests yet */
> + WARN_ON_ONCE(i != HV_L1_TLB_FLUSH_FIFO);
> +
> + return &hv_vcpu->tlb_flush_fifo[i];
> +}
>
> static inline void kvm_hv_vcpu_empty_flush_tlb(struct kvm_vcpu *vcpu)
> {
> struct kvm_vcpu_hv_tlb_flush_fifo *tlb_flush_fifo;
> - struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
>
> - if (!hv_vcpu || !kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu))
> + if (!to_hv_vcpu(vcpu) || !kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu))
> return;
>
> - tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
> + tlb_flush_fifo = kvm_hv_get_tlb_flush_fifo(vcpu);
>
> kfifo_reset_out(&tlb_flush_fifo->entries);
> }
Looks great,
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
Best regards,
Maxim Levitsky
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