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    KVM: MMU: Fix mmu_shrink() so that it can free mmu pages as intended · 35f2d16b
    Takuya Yoshikawa 提交于
    Although the possible race described in
    
      commit 85b70591
      KVM: MMU: fix shrinking page from the empty mmu
    
    was correct, the real cause of that issue was a more trivial bug of
    mmu_shrink() introduced by
    
      commit 19526396
      KVM: MMU: do not iterate over all VMs in mmu_shrink()
    
    Here is the bug:
    
    	if (kvm->arch.n_used_mmu_pages > 0) {
    		if (!nr_to_scan--)
    			break;
    		continue;
    	}
    
    We skip VMs whose n_used_mmu_pages is not zero and try to shrink others:
    in other words we try to shrink empty ones by mistake.
    
    This patch reverses the logic so that mmu_shrink() can free pages from
    the first VM whose n_used_mmu_pages is not zero.  Note that we also add
    comments explaining the role of nr_to_scan which is not practically
    important now, hoping this will be improved in the future.
    Signed-off-by: NTakuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
    Cc: Gleb Natapov <gleb@redhat.com>
    Signed-off-by: NAvi Kivity <avi@redhat.com>
    35f2d16b
mmu.c 101.5 KB