linux-kernel - Re: [PATCH 2/4] KVM: PPC: Book3S HV: Improve kvmppc_allocate_hpt()/kvmppc_free

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Message-ID: <20171130034558.GP3023@umbus.fritz.box>
Date:   Thu, 30 Nov 2017 14:45:58 +1100
From:   David Gibson <david@...son.dropbear.id.au>
To:     Serhii Popovych <spopovyc@...hat.com>
Cc:     linux-kernel@...r.kernel.org, michael@...erman.id.au,
        paulus@...ba.org, linuxppc-dev@...ts.ozlabs.org,
        kvm-ppc@...r.kernel.org
Subject: Re: [PATCH 2/4] KVM: PPC: Book3S HV: Improve
 kvmppc_allocate_hpt()/kvmppc_free_hpt()

On Wed, Nov 29, 2017 at 11:38:24AM -0500, Serhii Popovych wrote:
> There are several points of improvements:
> 
>   1) Make kvmppc_free_hpt() check if allocation is made before attempt
>      to release. This follows kfree(p) semantics where p == NULL.
> 
>   2) Return initialized @info parameter from kvmppc_allocate_hpt()
>      even if allocation fails.
> 
>      This allows to use kvmppc_free_hpt() in the caller without
>      checking that preceded kvmppc_allocate_hpt() was successful
> 
>          p = kmalloc(size, gfp);
>          kfree(p);
> 
>      which is correct for both p != NULL and p == NULL. Followup
>      change will rely on this behaviour.
> 
>   3) Better code reuse: kvmppc_free_hpt() can be reused on error
>      path in kvmppc_allocate_hpt() to avoid code duplication.
> 
>   4) No need to check for !hpt if allocated from CMA: neither
>      pfn_to_kaddr() nor page_to_pfn() is 0 in case of page != NULL.
> 
> Signed-off-by: Serhii Popovych <spopovyc@...hat.com>

Reviewed-by: David Gibson <david@...son.dropbear.id.au>

> ---
>  arch/powerpc/kvm/book3s_64_mmu_hv.c | 54 ++++++++++++++++++-------------------
>  1 file changed, 26 insertions(+), 28 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index 0534aab..3e9abd9 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -82,47 +82,44 @@ struct kvm_resize_hpt {
>  int kvmppc_allocate_hpt(struct kvm_hpt_info *info, u32 order)
>  {
>  	unsigned long hpt = 0;
> -	int cma = 0;
> -	struct page *page = NULL;
> -	struct revmap_entry *rev;
> +	int err, cma = 0;
> +	struct page *page;
> +	struct revmap_entry *rev = NULL;
>  	unsigned long npte;
>  
> +	err = -EINVAL;
>  	if ((order < PPC_MIN_HPT_ORDER) || (order > PPC_MAX_HPT_ORDER))
> -		return -EINVAL;
> +		goto out;
>  
> +	err = -ENOMEM;
>  	page = kvm_alloc_hpt_cma(1ul << (order - PAGE_SHIFT));
>  	if (page) {
>  		hpt = (unsigned long)pfn_to_kaddr(page_to_pfn(page));
>  		memset((void *)hpt, 0, (1ul << order));
>  		cma = 1;
> -	}
> -
> -	if (!hpt)
> +	} else {
>  		hpt = __get_free_pages(GFP_KERNEL|__GFP_ZERO|__GFP_RETRY_MAYFAIL
>  				       |__GFP_NOWARN, order - PAGE_SHIFT);
> -
> -	if (!hpt)
> -		return -ENOMEM;
> +		if (!hpt)
> +			goto out;
> +	}
>  
>  	/* HPTEs are 2**4 bytes long */
>  	npte = 1ul << (order - 4);
>  
>  	/* Allocate reverse map array */
> -	rev = vmalloc(sizeof(struct revmap_entry) * npte);
> -	if (!rev) {
> -		if (cma)
> -			kvm_free_hpt_cma(page, 1 << (order - PAGE_SHIFT));
> -		else
> -			free_pages(hpt, order - PAGE_SHIFT);
> -		return -ENOMEM;
> -	}
> -
> +	rev = vmalloc(sizeof(*rev) * npte);
> +	if (rev)
> +		err = 0;
> +out:
>  	info->order = order;
>  	info->virt = hpt;
>  	info->cma = cma;
>  	info->rev = rev;
>  
> -	return 0;
> +	if (err)
> +		kvmppc_free_hpt(info);
> +	return err;
>  }
>  
>  void kvmppc_set_hpt(struct kvm *kvm, struct kvm_hpt_info *info)
> @@ -190,12 +187,14 @@ void kvmppc_free_hpt(struct kvm_hpt_info *info)
>  {
>  	vfree(info->rev);
>  	info->rev = NULL;
> -	if (info->cma)
> -		kvm_free_hpt_cma(virt_to_page(info->virt),
> -				 1 << (info->order - PAGE_SHIFT));
> -	else if (info->virt)
> -		free_pages(info->virt, info->order - PAGE_SHIFT);
> -	info->virt = 0;
> +	if (info->virt) {
> +		if (info->cma)
> +			kvm_free_hpt_cma(virt_to_page(info->virt),
> +					 1 << (info->order - PAGE_SHIFT));
> +		else
> +			free_pages(info->virt, info->order - PAGE_SHIFT);
> +		info->virt = 0;
> +	}
>  	info->order = 0;
>  }
>  
> @@ -1423,8 +1422,7 @@ static void resize_hpt_release(struct kvm *kvm, struct kvm_resize_hpt *resize)
>  	if (!resize)
>  		return;
>  
> -	if (resize->hpt.virt)
> -		kvmppc_free_hpt(&resize->hpt);
> +	kvmppc_free_hpt(&resize->hpt);
>  
>  	kvm->arch.resize_hpt = NULL;
>  	kfree(resize);

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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