On Mon, Sep 24, 2012 at 07:49:37PM +0800, Xiao Guangrong wrote: > On 09/24/2012 07:24 PM, Gleb Natapov wrote: > > On Mon, Sep 24, 2012 at 12:59:32PM +0800, Xiao Guangrong wrote: > >> On 09/23/2012 05:13 PM, Gleb Natapov wrote: > >>> On Fri, Sep 21, 2012 at 02:57:19PM +0800, 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 > >>>> spte > >>>> > >>> Wouldn't it be better to move the check into kvm_release_pfn_clean()? > >> > >> I think there is no reason for us to prefer to adding this branch in > >> the common code. :) > > > > Is the function performance critical? Is function called without the check > > on a hot path? The function already contains much heavier kvm_is_mmio_pfn() > > check. If most/all function invocation require check before call it's > > better to move it inside. > > It is not most/all functions need do this check - it is only needed on x86 mmu > page-fault/prefetch path. At least on x86 there 7 calls to kvm_release_pfn_clean(), 5 of them are guarded by is_noslot_pfn() (after this patch) and one by even stronger is_error_pfn(). I guess when/if other architectures will add MMIO MMU caching they will need to guard kvm_release_pfn_clean() by is_noslot_pfn() too in most cases. I am not insisting, but as this patch shows it is easy to miss the check before calling the function. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
