[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <56F54614.3050300@linux.intel.com>
Date: Fri, 25 Mar 2016 22:07:16 +0800
From: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] KVM: MMU: reduce the size of mmu_page_path
On 03/25/2016 09:56 PM, Paolo Bonzini wrote:
>
>
> On 25/03/2016 14:48, Xiao Guangrong wrote:
>>>>
>>>
>>> This patch and the previous one are basically redoing commit
>>> 0a47cd85833e ("KVM: MMU: Fix ubsan warnings", 2016-03-04). While you
>>> find your version easier to understand, I of course find mine easier.
>>>
>>> Rather than getting stuck in a ko fight, the solution is to stick with
>>> the code in KVM and add comments. I'll give it a try...
>>
>> If you do not like this one, we can just make the .index is
>> [PT64_ROOT_LEVEL - 1] and keep the sentinel in .parents[], that little
>> change and nice code shape.
>
> I suppose you'd have something like this then:
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 70e95d097ef1..15e1735a2e3a 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1980,7 +1980,7 @@ static bool kvm_sync_pages(struct kvm_vcpu *vcpu, gfn_t gfn,
>
> struct mmu_page_path {
> struct kvm_mmu_page *parent[PT64_ROOT_LEVEL];
> - unsigned int idx[PT64_ROOT_LEVEL];
> + unsigned int idx[PT64_ROOT_LEVEL-1];
> };
>
> #define for_each_sp(pvec, sp, parents, i) \
> @@ -2037,13 +2037,14 @@ static void mmu_pages_clear_parents(struct mmu_page_path *parents)
> {
> struct kvm_mmu_page *sp;
> unsigned int level = 0;
> + unsigned int idx;
>
> do {
> - unsigned int idx = parents->idx[level];
> sp = parents->parent[level];
> - if (!sp)
> + if (!sp || WARN_ON(level == PT64_ROOT_LEVEL-1))
> return;
>
> + idx = parents->idx[level];
> WARN_ON(idx == INVALID_INDEX);
> clear_unsync_child_bit(sp, idx);
> level++;
>
Yes, exactly.
[ actually, we can keep mmu_pages_clear_parents() unchanged ]
> By making the arrays the same size, the effect of the sentinel seems
> clearer to me. It doesn't seem worth 4 bytes (and strictly speaking
> those 4 bytes would be there anyway due to padding)...
The sentinel is NULL forever so it can not go to the inner loop anyway...
Okay, i am not strong opinion on it, it is not a big deal. Let's
happily drop it if you really dislike it. :)
Powered by blists - more mailing lists