From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Subject: Re: [PATCH v5 04/13] KVM: Introduce a new guest mapping API Date: Thu, 10 Jan 2019 14:07:04 +0100 Message-ID: <4e9a23bb-bf13-33e5-8d00-1bb5a59e91bb@redhat.com> References: <1547026933-31226-1-git-send-email-karahmed@amazon.de> <1547026933-31226-5-git-send-email-karahmed@amazon.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit To: KarimAllah Ahmed , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, pbonzini@redhat.com, rkrcmar@redhat.com Return-path: In-Reply-To: <1547026933-31226-5-git-send-email-karahmed@amazon.de> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 09.01.19 10:42, KarimAllah Ahmed wrote: > In KVM, specially for nested guests, there is a dominant pattern of: > > => map guest memory -> do_something -> unmap guest memory > > In addition to all this unnecessarily noise in the code due to boiler plate > code, most of the time the mapping function does not properly handle memory > that is not backed by "struct page". This new guest mapping API encapsulate > most of this boiler plate code and also handles guest memory that is not > backed by "struct page". > > The current implementation of this API is using memremap for memory that is > not backed by a "struct page" which would lead to a huge slow-down if it > was used for high-frequency mapping operations. The API does not have any > effect on current setups where guest memory is backed by a "struct page". > Further patches are going to also introduce a pfn-cache which would > significantly improve the performance of the memremap case. > > Signed-off-by: KarimAllah Ahmed > --- > v3 -> v4: > - Update the commit message. > v1 -> v2: > - Drop the caching optimization (pbonzini) > - Use 'hva' instead of 'kaddr' (pbonzini) > - Return 0/-EINVAL/-EFAULT instead of true/false. -EFAULT will be used for > AMD patch (pbonzini) > - Introduce __kvm_map_gfn which accepts a memory slot and use it (pbonzini) > - Only clear map->hva instead of memsetting the whole structure. > - Drop kvm_vcpu_map_valid since it is no longer used. > - Fix EXPORT_MODULE naming. > --- > include/linux/kvm_host.h | 9 ++++++++ > virt/kvm/kvm_main.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 62 insertions(+) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index c38cc5e..8a2f5fa 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -205,6 +205,13 @@ enum { > READING_SHADOW_PAGE_TABLES, > }; > > +struct kvm_host_map { > + struct page *page; Can you add somme comments to what it means when there is a page vs. when there is none? > + void *hva; > + kvm_pfn_t pfn; > + kvm_pfn_t gfn; > +}; > + > /* > * Sometimes a large or cross-page mmio needs to be broken up into separate > * exits for userspace servicing. > @@ -710,7 +717,9 @@ struct kvm_memslots *kvm_vcpu_memslots(struct kvm_vcpu *vcpu); > struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn); > kvm_pfn_t kvm_vcpu_gfn_to_pfn_atomic(struct kvm_vcpu *vcpu, gfn_t gfn); > kvm_pfn_t kvm_vcpu_gfn_to_pfn(struct kvm_vcpu *vcpu, gfn_t gfn); > +int kvm_vcpu_map(struct kvm_vcpu *vcpu, gpa_t gpa, struct kvm_host_map *map); > struct page *kvm_vcpu_gfn_to_page(struct kvm_vcpu *vcpu, gfn_t gfn); > +void kvm_vcpu_unmap(struct kvm_host_map *map, bool dirty); > unsigned long kvm_vcpu_gfn_to_hva(struct kvm_vcpu *vcpu, gfn_t gfn); > unsigned long kvm_vcpu_gfn_to_hva_prot(struct kvm_vcpu *vcpu, gfn_t gfn, bool *writable); > int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data, int offset, > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 1f888a1..4d8f2e3 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -1733,6 +1733,59 @@ struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn) > } > EXPORT_SYMBOL_GPL(gfn_to_page); > > +static int __kvm_map_gfn(struct kvm_memory_slot *slot, gfn_t gfn, > + struct kvm_host_map *map) > +{ > + kvm_pfn_t pfn; > + void *hva = NULL; > + struct page *page = NULL; nit: I prefer these in a growing line-length fashion. > + > + pfn = gfn_to_pfn_memslot(slot, gfn); > + if (is_error_noslot_pfn(pfn)) > + return -EINVAL; > + > + if (pfn_valid(pfn)) { > + page = pfn_to_page(pfn); > + hva = kmap(page); > + } else { > + hva = memremap(pfn_to_hpa(pfn), PAGE_SIZE, MEMREMAP_WB); > + } > + > + if (!hva) > + return -EFAULT; > + > + map->page = page; > + map->hva = hva; > + map->pfn = pfn; > + map->gfn = gfn; > + > + return 0; > +} > + > +int kvm_vcpu_map(struct kvm_vcpu *vcpu, gfn_t gfn, struct kvm_host_map *map) > +{ > + return __kvm_map_gfn(kvm_vcpu_gfn_to_memslot(vcpu, gfn), gfn, map); > +} > +EXPORT_SYMBOL_GPL(kvm_vcpu_map); > + > +void kvm_vcpu_unmap(struct kvm_host_map *map, bool dirty) > +{ > + if (!map->hva) > + return; > + > + if (map->page) > + kunmap(map->page); > + else > + memunmap(map->hva); > + > + if (dirty) I am wondering if this would also be the right place for kvm_vcpu_mark_page_dirty() to mark the page dirty for migration. > + kvm_release_pfn_dirty(map->pfn); > + else > + kvm_release_pfn_clean(map->pfn); > + map->hva = NULL; > +} > +EXPORT_SYMBOL_GPL(kvm_vcpu_unmap); > + > struct page *kvm_vcpu_gfn_to_page(struct kvm_vcpu *vcpu, gfn_t gfn) > { > kvm_pfn_t pfn; > -- Thanks, David / dhildenb