Messages in this thread | | | Subject | Re: [PATCH 2/2] KVM: arm64: Skip the cache flush when coalescing tables into a block | From | "wangyanan (Y)" <> | Date | Tue, 9 Mar 2021 17:02:29 +0800 |
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On 2021/3/9 16:43, Marc Zyngier wrote: > On Tue, 09 Mar 2021 08:34:43 +0000, > "wangyanan (Y)" <wangyanan55@huawei.com> wrote: >> >> On 2021/3/9 0:34, Will Deacon wrote: >>> On Mon, Jan 25, 2021 at 10:10:44PM +0800, Yanan Wang wrote: >>>> After dirty-logging is stopped for a VM configured with huge mappings, >>>> KVM will recover the table mappings back to block mappings. As we only >>>> replace the existing page tables with a block entry and the cacheability >>>> has not been changed, the cache maintenance opreations can be skipped. >>>> >>>> Signed-off-by: Yanan Wang <wangyanan55@huawei.com> >>>> --- >>>> arch/arm64/kvm/mmu.c | 12 +++++++++--- >>>> 1 file changed, 9 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c >>>> index 8e8549ea1d70..37b427dcbc4f 100644 >>>> --- a/arch/arm64/kvm/mmu.c >>>> +++ b/arch/arm64/kvm/mmu.c >>>> @@ -744,7 +744,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >>>> { >>>> int ret = 0; >>>> bool write_fault, writable, force_pte = false; >>>> - bool exec_fault; >>>> + bool exec_fault, adjust_hugepage; >>>> bool device = false; >>>> unsigned long mmu_seq; >>>> struct kvm *kvm = vcpu->kvm; >>>> @@ -872,12 +872,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >>>> mark_page_dirty(kvm, gfn); >>>> } >>>> - if (fault_status != FSC_PERM && !device) >>>> + /* >>>> + * There is no necessity to perform cache maintenance operations if we >>>> + * will only replace the existing table mappings with a block mapping. >>>> + */ >>>> + adjust_hugepage = fault_granule < vma_pagesize ? true : false; >>> nit: you don't need the '? true : false' part >>> >>> That said, your previous patch checks for 'fault_granule > vma_pagesize', >>> so I'm not sure the local variable helps all that much here because it >>> obscures the size checks in my opinion. It would be more straight-forward >>> if we could structure the logic as: >>> >>> >>> if (fault_granule < vma_pagesize) { >>> >>> } else if (fault_granule > vma_page_size) { >>> >>> } else { >>> >>> } >>> >>> With some comments describing what we can infer about the memcache and cache >>> maintenance requirements for each case. >> Thanks for your suggestion here, Will. >> But I have resent another newer series [1] (KVM: arm64: Improve >> efficiency of stage2 page table) >> recently, which has the same theme but different solutions that I >> think are better. >> [1] >> https://lore.kernel.org/lkml/20210208112250.163568-1-wangyanan55@huawei.com/ >> >> Could you please comment on that series ? I think it can be found in >> your inbox :). > There were already a bunch of comments on that series, and I stopped > at the point where the cache maintenance was broken. Please respin > that series if you want further feedback on it. Ok, I will send a new version later. > > In the future, if you deprecate a series (which is completely > understandable), please leave a note on the list with a pointer to the > new series so that people don't waste time reviewing an obsolete > series. Or post the new series with a new version number so that it is > obvious that the original series has been superseded. I apologize for this, I will be more careful in the future.
Thanks,
Yanan > Thanks, > > M. >
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