linux-kernel - Re: [PATCH] KVM swapping with MMU Notifiers V7

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Message-Id: <20080216030817.965ff1f7.akpm@linux-foundation.org>
Date:	Sat, 16 Feb 2008 03:08:17 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrea Arcangeli <andrea@...ranet.com>
Cc:	Christoph Lameter <clameter@....com>, Robin Holt <holt@....com>,
	Avi Kivity <avi@...ranet.com>, Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	general@...ts.openfabrics.org,
	Steve Wise <swise@...ngridcomputing.com>,
	Roland Dreier <rdreier@...co.com>,
	Kanoj Sarcar <kanojsarcar@...oo.com>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [PATCH] KVM swapping with MMU Notifiers V7

On Sat, 16 Feb 2008 11:48:27 +0100 Andrea Arcangeli <andrea@...ranet.com> wrote:

> +void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
> +					   struct mm_struct *mm,
> +					   unsigned long start, unsigned long end,
> +					   int lock)
> +{
> +	for (; start < end; start += PAGE_SIZE)
> +		kvm_mmu_notifier_invalidate_page(mn, mm, start);
> +}
> +
> +static const struct mmu_notifier_ops kvm_mmu_notifier_ops = {
> +	.invalidate_page	= kvm_mmu_notifier_invalidate_page,
> +	.age_page		= kvm_mmu_notifier_age_page,
> +	.invalidate_range_end	= kvm_mmu_notifier_invalidate_range_end,
> +};

So this doesn't implement ->invalidate_range_start().

By what means does it prevent new mappings from being established in the
range after core mm has tried to call ->invalidate_rande_start()?
mmap_sem, I assume?


> +			/* set userspace_addr atomically for kvm_hva_to_rmapp */
> +			spin_lock(&kvm->mmu_lock);
> +			memslot->userspace_addr = userspace_addr;
> +			spin_unlock(&kvm->mmu_lock);

are you sure?  kvm_unmap_hva() and kvm_age_hva() read ->userspace_addr a
single time and it doesn't immediately look like there's a need to take the
lock here?


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