linux-kernel - Re: [PATCH v3 2/8] KVM: x86/mmu: Factor out allocating memslot rmap

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Date:   Fri, 7 May 2021 09:46:57 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Ben Gardon <bgardon@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Kai Huang <kai.huang@...el.com>,
        Keqian Zhu <zhukeqian1@...wei.com>
Subject: Re: [PATCH v3 2/8] KVM: x86/mmu: Factor out allocating memslot rmap

On 06.05.21 20:42, Ben Gardon wrote:
> Small refactor to facilitate allocating rmaps for all memslots at once.
> 
> No functional change expected.
> 
> Signed-off-by: Ben Gardon <bgardon@...gle.com>
> ---
>   arch/x86/kvm/x86.c | 41 ++++++++++++++++++++++++++++++++---------
>   1 file changed, 32 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5bcf07465c47..fc32a7dbe4c4 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10842,10 +10842,37 @@ void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
>   	kvm_page_track_free_memslot(slot);
>   }
>   
> +static int alloc_memslot_rmap(struct kvm_memory_slot *slot,
> +			      unsigned long npages)

I'd have called the functions memslot_rmap_alloc() and memslot_rmap_free()


> +{
> +	int i;
> +
> +	for (i = 0; i < KVM_NR_PAGE_SIZES; ++i) {
> +		int lpages;
> +		int level = i + 1;
> +
> +		lpages = gfn_to_index(slot->base_gfn + npages - 1,
> +				      slot->base_gfn, level) + 1;
> +
> +		slot->arch.rmap[i] =
> +			kvcalloc(lpages, sizeof(*slot->arch.rmap[i]),
> +				 GFP_KERNEL_ACCOUNT);
> +		if (!slot->arch.rmap[i])
> +			goto out_free;

you can just avoid the goto here and do the free_memslot_rmap() right away.

> +	}
> +
> +	return 0;
> +
> +out_free:
> +	free_memslot_rmap(slot);
> +	return -ENOMEM;
> +}
> +
>   static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
>   				      unsigned long npages)
>   {
>   	int i;
> +	int r;
>   
>   	/*
>   	 * Clear out the previous array pointers for the KVM_MR_MOVE case.  The
> @@ -10854,7 +10881,11 @@ static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
>   	 */
>   	memset(&slot->arch, 0, sizeof(slot->arch));
>   
> -	for (i = 0; i < KVM_NR_PAGE_SIZES; ++i) {
> +	r = alloc_memslot_rmap(slot, npages);
> +	if (r)
> +		return r;
> +
> +	for (i = 1; i < KVM_NR_PAGE_SIZES; ++i) {
>   		struct kvm_lpage_info *linfo;
>   		unsigned long ugfn;
>   		int lpages;
> @@ -10863,14 +10894,6 @@ static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
>   		lpages = gfn_to_index(slot->base_gfn + npages - 1,
>   				      slot->base_gfn, level) + 1;
>   
> -		slot->arch.rmap[i] =
> -			kvcalloc(lpages, sizeof(*slot->arch.rmap[i]),
> -				 GFP_KERNEL_ACCOUNT);
> -		if (!slot->arch.rmap[i])
> -			goto out_free;
> -		if (i == 0)
> -			continue;
> -
>   		linfo = kvcalloc(lpages, sizeof(*linfo), GFP_KERNEL_ACCOUNT);
>   		if (!linfo)
>   			goto out_free;
> 

apart from that LGTM

-- 
Thanks,

David / dhildenb