linux-kernel - Re: [PATCH] KVM: replace large kvmalloc allocation with vmalloc

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Date:   Fri, 15 Oct 2021 17:28:09 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        syzbot+e0de2333cbf95ea473e8@...kaller.appspotmail.com
Subject: Re: [PATCH] KVM: replace large kvmalloc allocation with vmalloc

On Fri, Oct 15, 2021, Paolo Bonzini wrote:
> diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
> index 21427e84a82e..0d9842472288 100644
> --- a/arch/x86/kvm/mmu/page_track.c
> +++ b/arch/x86/kvm/mmu/page_track.c
> @@ -36,8 +36,7 @@ int kvm_page_track_create_memslot(struct kvm_memory_slot *slot,
>  
>  	for (i = 0; i < KVM_PAGE_TRACK_MAX; i++) {
>  		slot->arch.gfn_track[i] =
> -			kvcalloc(npages, sizeof(*slot->arch.gfn_track[i]),
> -				 GFP_KERNEL_ACCOUNT);
> +			vcalloc(npages, sizeof(*slot->arch.gfn_track[i]));

This loses the memcg accounting, which is somewhat important for the theoretical
4MiB allocations :-)

Maybe split out the introduction of vcalloc() to a separate patch (or two) and
introduce additional helpers to allow passing in gfp_t to e.g. __vzalloc()?

>  		if (!slot->arch.gfn_track[i])
>  			goto track_free;
>  	}
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index aabd3a2ec1bc..07f5760ea30c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -11394,7 +11394,7 @@ static int memslot_rmap_alloc(struct kvm_memory_slot *slot,
>  
>  		WARN_ON(slot->arch.rmap[i]);
>  
> -		slot->arch.rmap[i] = kvcalloc(lpages, sz, GFP_KERNEL_ACCOUNT);
> +		slot->arch.rmap[i] = vcalloc(lpages, sz);
>  		if (!slot->arch.rmap[i]) {
>  			memslot_rmap_free(slot);
>  			return -ENOMEM;
> @@ -11475,7 +11475,7 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
>  
>  		lpages = __kvm_mmu_slot_lpages(slot, npages, level);
>  
> -		linfo = kvcalloc(lpages, sizeof(*linfo), GFP_KERNEL_ACCOUNT);
> +		linfo = vcalloc(lpages, sizeof(*linfo));
>  		if (!linfo)
>  			goto out_free;

All of the associated free paths should be converted to vfree().