linux-kernel - Re: [PATCH v10 05/39] KVM: x86: hyper-v: Handle HVCALL_FLUSH_VIRTUAL_ADDRESS

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Date:   Wed, 21 Sep 2022 17:00:33 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.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>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 05/39] KVM: x86: hyper-v: Handle
 HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST{,EX} calls gently

On Wed, Sep 21, 2022, Vitaly Kuznetsov wrote:
>  void kvm_hv_vcpu_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);
> +	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;
> +	}
> +	return;
> +
> +out_flush_all:
> +	kvm_vcpu_flush_tlb_guest(vcpu);
>  	kfifo_reset_out(&tlb_flush_fifo->entries);
>  }

If kvm_vcpu_flush_tlb_guest() is done as a fallback, then this can use -ENOSPC,
which again I like from a documentation perspective.

out_flush_all:
	kfifo_reset_out(&tlb_flush_fifo->entries);
	return -ENOSPC;