From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sean Christopherson Date: Thu, 06 Feb 2020 21:21:20 +0000 Subject: Re: [PATCH v5 15/19] KVM: Provide common implementation for generic dirty log functions Message-Id: <20200206212120.GF13067@linux.intel.com> List-Id: References: <20200121223157.15263-1-sean.j.christopherson@intel.com> <20200121223157.15263-16-sean.j.christopherson@intel.com> <20200206200200.GC700495@xz-x1> In-Reply-To: <20200206200200.GC700495@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Peter Xu Cc: Paolo Bonzini , Paul Mackerras , Christian Borntraeger , Janosch Frank , David Hildenbrand , Cornelia Huck , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Marc Zyngier , James Morse , Julien Thierry , Suzuki K Poulose , linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, Christoffer Dall , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= On Thu, Feb 06, 2020 at 03:02:00PM -0500, Peter Xu wrote: > On Tue, Jan 21, 2020 at 02:31:53PM -0800, Sean Christopherson wrote: > > [...] > > > -int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm, struct kvm_clear_dirty_log *log) > > +void kvm_arch_dirty_log_tlb_flush(struct kvm *kvm, > > + struct kvm_memory_slot *memslot) > > If it's to flush TLB for a memslot, shall we remove the "dirty_log" in > the name of the function, because it has nothing to do with dirty > logging any more? And... I kept the "dirty_log" to allow arch code to implement logic specific to a TLB flush during dirty logging, e.g. x86's lockdep assert on slots_lock. And similar to the issue with MIPS below, to deter usage of the hook for anything else, i.e. to nudge people to using kvm_flush_remote_tlbs() directly. > > { > > - struct kvm_memslots *slots; > > - struct kvm_memory_slot *memslot; > > - bool flush = false; > > - int r; > > - > > - mutex_lock(&kvm->slots_lock); > > - > > - r = kvm_clear_dirty_log_protect(kvm, log, &flush); > > - > > - if (flush) { > > - slots = kvm_memslots(kvm); > > - memslot = id_to_memslot(slots, log->slot); > > - > > - /* Let implementation handle TLB/GVA invalidation */ > > - kvm_mips_callbacks->flush_shadow_memslot(kvm, memslot); > > - } > > - > > - mutex_unlock(&kvm->slots_lock); > > - return r; > > + /* Let implementation handle TLB/GVA invalidation */ > > + kvm_mips_callbacks->flush_shadow_memslot(kvm, memslot); > > ... This may not directly related to the current patch, but I'm > confused on why MIPS cannot use kvm_flush_remote_tlbs() to flush TLBs. > I know nothing about MIPS code, but IIUC here flush_shadow_memslot() > is a heavier operation that will also invalidate the shadow pages. > Seems to be an overkill here when we only changed write permission of > the PTEs? I tried to check the first occurance (2a31b9db15353) but I > didn't find out any clue of it so far. > > But that matters to this patch because if MIPS can use > kvm_flush_remote_tlbs(), then we probably don't need this > arch-specific hook any more and we can directly call > kvm_flush_remote_tlbs() after sync dirty log when flush=true. Ya, the asid_flush_mask in kvm_vz_flush_shadow_all() is the only thing that prevents calling kvm_flush_remote_tlbs() directly, but I have no clue as to the important of that code. > > } > > > > long kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg) > > diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c > > index 97ce6c4f7b48..0adaf4791a6d 100644 > > --- a/arch/powerpc/kvm/book3s.c > > +++ b/arch/powerpc/kvm/book3s.c > > @@ -799,6 +799,11 @@ int kvmppc_core_check_requests(struct kvm_vcpu *vcpu) > > return vcpu->kvm->arch.kvm_ops->check_requests(vcpu); > > } > > > > +void kvm_arch_sync_dirty_log(struct kvm *kvm, struct kvm_memory_slot *memslot) > > Since at it, maybe we can start to use __weak attribute for new hooks > especially when it's empty for most archs? > > E.g., define: > > void __weak kvm_arch_sync_dirty_log(...) {} > > In the common code, then only define it again in arch that has > non-empty implementation of this method? I defer to Paolo, I'm indifferent at this stage.