linux-kernel - [PATCH 10/19] KVM: mmu_shrink: kvm_mmu_zap_page requires slots

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Message-Id: <1216123958-10717-11-git-send-email-avi@qumranet.com>
Date:	Tue, 15 Jul 2008 15:12:29 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	kvm@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Marcelo Tosatti <mtosatti@...hat.com>
Subject: [PATCH 10/19] KVM: mmu_shrink: kvm_mmu_zap_page requires slots_lock to be held

From: Marcelo Tosatti <mtosatti@...hat.com>

kvm_mmu_zap_page() needs slots lock held (rmap_remove->gfn_to_memslot,
for example).

Since kvm_lock spinlock is held in mmu_shrink(), do a non-blocking
down_read_trylock().

Untested.

Signed-off-by: Avi Kivity <avi@...ranet.com>
---
 arch/x86/kvm/mmu.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 1fd8e3b..ff7cf63 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1987,6 +1987,8 @@ static int mmu_shrink(int nr_to_scan, gfp_t gfp_mask)
 	list_for_each_entry(kvm, &vm_list, vm_list) {
 		int npages;
 
+		if (!down_read_trylock(&kvm->slots_lock))
+			continue;
 		spin_lock(&kvm->mmu_lock);
 		npages = kvm->arch.n_alloc_mmu_pages -
 			 kvm->arch.n_free_mmu_pages;
@@ -1999,6 +2001,7 @@ static int mmu_shrink(int nr_to_scan, gfp_t gfp_mask)
 		nr_to_scan--;
 
 		spin_unlock(&kvm->mmu_lock);
+		up_read(&kvm->slots_lock);
 	}
 	if (kvm_freed)
 		list_move_tail(&kvm_freed->vm_list, &vm_list);
-- 
1.5.6.1

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