Re: [PATCH 4/7] kvm mmu: implement necessary data structures for second huge page accounting

From: Avi Kivity <avi@redhat.com>
To: Joerg Roedel <joerg.roedel@amd.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/7] kvm mmu: implement necessary data structures for second huge page accounting
Date: Sun, 29 Mar 2009 16:26:46 +0300	[thread overview]
Message-ID: <49CF7716.1000008@redhat.com> (raw)
In-Reply-To: <1238164319-16092-5-git-send-email-joerg.roedel@amd.com>

Joerg Roedel wrote:
> This patch adds the necessary data structures to take care of write
> protections in place within a second huge page sized page.
>
>
> +#ifdef KVM_PAGES_PER_LHPAGE
> +	if (npages && !new.hpage_info) {
> +		int hugepages = npages / KVM_PAGES_PER_LHPAGE;
> +		if (npages % KVM_PAGES_PER_LHPAGE)
> +			hugepages++;
> +		if (base_gfn % KVM_PAGES_PER_LHPAGE)
> +			hugepages++;
>   

Consider a slot with base_gfn == 1 and npages == 1.  This will have 
hugepages == 2, which is wrong.

I think the right calculation is

  ((base_gfn + npages - 1) / N) - (base_gfn / N) + 1

i.e. index of last page, plus one so we can store it.

The small huge page calculation is off as well.

> +
> +		new.hpage_info = vmalloc(hugepages * sizeof(*new.hpage_info));
> +
> +		if (!new.hpage_info)
> +			goto out_free;
> +
> +		memset(new.hpage_info, 0, hugepages * sizeof(*new.hpage_info));
> +
> +		if (base_gfn % KVM_PAGES_PER_LHPAGE)
> +			new.hpage_info[0].write_count = 1;
> +		if ((base_gfn+npages) % KVM_PAGES_PER_LHPAGE)
> +			new.hpage_info[hugepages-1].write_count = 1;
> +	}
> +#endif
> +
>   

-- 
error compiling committee.c: too many arguments to function