Re: [PATCH 1/3] KVM: MMU: release noslot pfn on the fail path properly
From: Avi Kivity
Date: Mon Sep 10 2012 - 05:02:32 EST
On 09/10/2012 11:37 AM, Xiao Guangrong wrote:
> On 09/10/2012 04:22 PM, Avi Kivity wrote:
>> On 09/07/2012 09:13 AM, Xiao Guangrong wrote:
>>> We can not directly call kvm_release_pfn_clean to release the pfn
>>> since we can meet noslot pfn which is used to cache mmio info into
>>> Introduce mmu_release_pfn_clean to do this kind of thing
>>> Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
>>> arch/x86/kvm/mmu.c | 19 ++++++++++++++-----
>>> arch/x86/kvm/paging_tmpl.h | 4 ++--
>>> 2 files changed, 16 insertions(+), 7 deletions(-)
>>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>>> index 399c177..3c10bca 100644
>>> --- a/arch/x86/kvm/mmu.c
>>> +++ b/arch/x86/kvm/mmu.c
>>> @@ -2432,6 +2432,16 @@ done:
>>> return ret;
>>> + * The primary user is page fault path which call it to properly
>>> + * release noslot_pfn.
>>> + */
>>> +static void mmu_release_pfn_clean(pfn_t pfn)
>>> + if (!is_error_pfn(pfn))
>>> + kvm_release_pfn_clean(pfn);
>> Too many APIs, each slightly different. How do I know which one to call?
> It is only used in mmu and it is a static function.
Still, how do I know which one to call? The name tells me nothing.
When I read the code, how do I know if a call is correct or not?
>> Please change kvm_release_pfn_*() instead, calling some arch hook (or
>> even #ifdef CONFIG_KVM_HAS_FAST_MMIO) to check for the special case.
> We only need to call it on page fault path. If we change the common API
> other x86 components have to suffer from it.
This way, I have to suffer from it.
btw, what about another approach, to avoid those paths completely?
Avoid calling __direct_map() with error_pfn, and jump to a label after
kvm_release_pfn_clean() in page_fault(), etc?
error compiling committee.c: too many arguments to function
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