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Date:   Fri, 27 May 2022 16:39:30 +0800
From:   Yuan Yao <yuan.yao@linux.intel.com>
To:     Vitaly Kuznetsov <vkuznets@redhat.com>
Cc:     kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Maxim Levitsky <mlevitsk@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Michael Kelley <mikelley@microsoft.com>,
        Siddharth Chandrasekaran <sidcha@amazon.de>,
        linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 05/37] KVM: x86: hyper-v: Handle
 HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST{,EX} calls gently
Message-ID: <20220527083930.okdenkvxephom5wq@yy-desk-7060>
References: <20220525090133.1264239-1-vkuznets@redhat.com>
 <20220525090133.1264239-6-vkuznets@redhat.com>
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On Wed, May 25, 2022 at 11:01:01AM +0200, Vitaly Kuznetsov wrote:
> Currently, HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST{,EX} calls are handled
> the exact same way as HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE{,EX}: by
> flushing the whole VPID and this is sub-optimal. Switch to handling
> these requests with 'flush_tlb_gva()' hooks instead. Use the newly
> introduced TLB flush fifo to queue the requests.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  arch/x86/kvm/hyperv.c | 102 +++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 90 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 762b0b699fdf..576749973727 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1806,32 +1806,84 @@ static u64 kvm_get_sparse_vp_set(struct kvm *kvm, struct kvm_hv_hcall *hc,
>  				  sparse_banks, consumed_xmm_halves, offset);
>  }
>
> -static void hv_tlb_flush_enqueue(struct kvm_vcpu *vcpu)
> +static int kvm_hv_get_tlb_flush_entries(struct kvm *kvm, struct kvm_hv_hcall *hc, u64 entries[],
> +					int consumed_xmm_halves, gpa_t offset)
> +{
> +	return kvm_hv_get_hc_data(kvm, hc, hc->rep_cnt, hc->rep_cnt,
> +				  entries, consumed_xmm_halves, offset);
> +}
> +
> +static void hv_tlb_flush_enqueue(struct kvm_vcpu *vcpu, u64 *entries, int count)
>  {
>  	struct kvm_vcpu_hv_tlb_flush_fifo *tlb_flush_fifo;
>  	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
>  	u64 entry = KVM_HV_TLB_FLUSHALL_ENTRY;
> +	unsigned long flags;
>
>  	if (!hv_vcpu)
>  		return;
>
>  	tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
>
> -	kfifo_in_spinlocked(&tlb_flush_fifo->entries, &entry, 1, &tlb_flush_fifo->write_lock);
> +	spin_lock_irqsave(&tlb_flush_fifo->write_lock, flags);
> +
> +	/*
> +	 * All entries should fit on the fifo leaving one free for 'flush all'
> +	 * entry in case another request comes in. In case there's not enough
> +	 * space, just put 'flush all' entry there.
> +	 */
> +	if (count && entries && count < kfifo_avail(&tlb_flush_fifo->entries)) {
> +		WARN_ON(kfifo_in(&tlb_flush_fifo->entries, entries, count) != count);
> +		goto out_unlock;
> +	}
> +
> +	/*
> +	 * Note: full fifo always contains 'flush all' entry, no need to check the
> +	 * return value.
> +	 */
> +	kfifo_in(&tlb_flush_fifo->entries, &entry, 1);
> +
> +out_unlock:
> +	spin_unlock_irqrestore(&tlb_flush_fifo->write_lock, flags);
>  }
>
>  void kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu)

Where's the caller to this kvm_hv_vcpu_flush_tlb() ?
I didn't see th caller in patch 1-22 and remains are
self-testing patches, any thing I missed ?

>  {
>  	struct kvm_vcpu_hv_tlb_flush_fifo *tlb_flush_fifo;
>  	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> +	u64 entries[KVM_HV_TLB_FLUSH_FIFO_SIZE];
> +	int i, j, count;
> +	gva_t gva;
>
> -	kvm_vcpu_flush_tlb_guest(vcpu);
> -
> -	if (!hv_vcpu)
> +	if (!tdp_enabled || !hv_vcpu) {
> +		kvm_vcpu_flush_tlb_guest(vcpu);
>  		return;
> +	}
>
>  	tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
>
> +	count = kfifo_out(&tlb_flush_fifo->entries, entries, KVM_HV_TLB_FLUSH_FIFO_SIZE);
> +
> +	for (i = 0; i < count; i++) {
> +		if (entries[i] == KVM_HV_TLB_FLUSHALL_ENTRY)
> +			goto out_flush_all;
> +
> +		/*
> +		 * Lower 12 bits of 'address' encode the number of additional
> +		 * pages to flush.
> +		 */
> +		gva = entries[i] & PAGE_MASK;
> +		for (j = 0; j < (entries[i] & ~PAGE_MASK) + 1; j++)
> +			static_call(kvm_x86_flush_tlb_gva)(vcpu, gva + j * PAGE_SIZE);
> +
> +		++vcpu->stat.tlb_flush;
> +	}
> +	goto out_empty_ring;
> +
> +out_flush_all:
> +	kvm_vcpu_flush_tlb_guest(vcpu);
> +
> +out_empty_ring:
>  	kfifo_reset_out(&tlb_flush_fifo->entries);
>  }
>
> @@ -1841,11 +1893,21 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>  	struct hv_tlb_flush_ex flush_ex;
>  	struct hv_tlb_flush flush;
>  	DECLARE_BITMAP(vcpu_mask, KVM_MAX_VCPUS);
> +	/*
> +	 * Normally, there can be no more than 'KVM_HV_TLB_FLUSH_FIFO_SIZE'
> +	 * entries on the TLB flush fifo. The last entry, however, needs to be
> +	 * always left free for 'flush all' entry which gets placed when
> +	 * there is not enough space to put all the requested entries.
> +	 */
> +	u64 __tlb_flush_entries[KVM_HV_TLB_FLUSH_FIFO_SIZE - 1];
> +	u64 *tlb_flush_entries;
>  	u64 valid_bank_mask;
>  	u64 sparse_banks[KVM_HV_MAX_SPARSE_VCPU_SET_BITS];
>  	struct kvm_vcpu *v;
>  	unsigned long i;
>  	bool all_cpus;
> +	int consumed_xmm_halves = 0;
> +	gpa_t data_offset;
>
>  	/*
>  	 * The Hyper-V TLFS doesn't allow more than 64 sparse banks, e.g. the
> @@ -1861,10 +1923,12 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>  			flush.address_space = hc->ingpa;
>  			flush.flags = hc->outgpa;
>  			flush.processor_mask = sse128_lo(hc->xmm[0]);
> +			consumed_xmm_halves = 1;
>  		} else {
>  			if (unlikely(kvm_read_guest(kvm, hc->ingpa,
>  						    &flush, sizeof(flush))))
>  				return HV_STATUS_INVALID_HYPERCALL_INPUT;
> +			data_offset = sizeof(flush);
>  		}
>
>  		trace_kvm_hv_flush_tlb(flush.processor_mask,
> @@ -1888,10 +1952,12 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>  			flush_ex.flags = hc->outgpa;
>  			memcpy(&flush_ex.hv_vp_set,
>  			       &hc->xmm[0], sizeof(hc->xmm[0]));
> +			consumed_xmm_halves = 2;
>  		} else {
>  			if (unlikely(kvm_read_guest(kvm, hc->ingpa, &flush_ex,
>  						    sizeof(flush_ex))))
>  				return HV_STATUS_INVALID_HYPERCALL_INPUT;
> +			data_offset = sizeof(flush_ex);
>  		}
>
>  		trace_kvm_hv_flush_tlb_ex(flush_ex.hv_vp_set.valid_bank_mask,
> @@ -1907,25 +1973,37 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>  			return HV_STATUS_INVALID_HYPERCALL_INPUT;
>
>  		if (all_cpus)
> -			goto do_flush;
> +			goto read_flush_entries;
>
>  		if (!hc->var_cnt)
>  			goto ret_success;
>
> -		if (kvm_get_sparse_vp_set(kvm, hc, sparse_banks, 2,
> -					  offsetof(struct hv_tlb_flush_ex,
> -						   hv_vp_set.bank_contents)))
> +		if (kvm_get_sparse_vp_set(kvm, hc, sparse_banks, consumed_xmm_halves,
> +					  data_offset))
> +			return HV_STATUS_INVALID_HYPERCALL_INPUT;
> +		data_offset += hc->var_cnt * sizeof(sparse_banks[0]);
> +		consumed_xmm_halves += hc->var_cnt;
> +	}
> +
> +read_flush_entries:
> +	if (hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE ||
> +	    hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX ||
> +	    hc->rep_cnt > ARRAY_SIZE(__tlb_flush_entries)) {
> +		tlb_flush_entries = NULL;
> +	} else {
> +		if (kvm_hv_get_tlb_flush_entries(kvm, hc, __tlb_flush_entries,
> +						consumed_xmm_halves, data_offset))
>  			return HV_STATUS_INVALID_HYPERCALL_INPUT;
> +		tlb_flush_entries = __tlb_flush_entries;
>  	}
>
> -do_flush:
>  	/*
>  	 * vcpu->arch.cr3 may not be up-to-date for running vCPUs so we can't
>  	 * analyze it here, flush TLB regardless of the specified address space.
>  	 */
>  	if (all_cpus) {
>  		kvm_for_each_vcpu(i, v, kvm)
> -			hv_tlb_flush_enqueue(v);
> +			hv_tlb_flush_enqueue(v, tlb_flush_entries, hc->rep_cnt);
>
>  		kvm_make_all_cpus_request(kvm, KVM_REQ_HV_TLB_FLUSH);
>  	} else {
> @@ -1935,7 +2013,7 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>  			v = kvm_get_vcpu(kvm, i);
>  			if (!v)
>  				continue;
> -			hv_tlb_flush_enqueue(v);
> +			hv_tlb_flush_enqueue(v, tlb_flush_entries, hc->rep_cnt);
>  		}
>
>  		kvm_make_vcpus_request_mask(kvm, KVM_REQ_HV_TLB_FLUSH, vcpu_mask);
> --
> 2.35.3
>