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Violators will be prosecuted for from ; Thu, 20 Feb 2020 13:31:36 -0000 Subject: Re: [PATCH v2 02/42] KVM: s390/interrupt: do not pin adapter interrupt pages References: <20200214222658.12946-1-borntraeger@de.ibm.com> <20200214222658.12946-3-borntraeger@de.ibm.com> <073d3666-480e-5ba5-a46b-4cbd615f4174@redhat.com> From: Christian Borntraeger Date: Thu, 20 Feb 2020 14:31:30 +0100 MIME-Version: 1.0 In-Reply-To: <073d3666-480e-5ba5-a46b-4cbd615f4174@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Message-Id: <45954200-ccfe-cfac-200d-d1b903d9fc39@de.ibm.com> Sender: linux-s390-owner@vger.kernel.org List-ID: To: David Hildenbrand , Janosch Frank Cc: KVM , Cornelia Huck , Thomas Huth , Ulrich Weigand , Claudio Imbrenda , linux-s390 , Michael Mueller , Vasily Gorbik On 17.02.20 10:43, David Hildenbrand wrote: > On 14.02.20 23:26, Christian Borntraeger wrote: >> From: Ulrich Weigand >> >> The adapter interrupt page containing the indicator bits is currently >> pinned. That means that a guest with many devices can pin a lot of >> memory pages in the host. This also complicates the reference tracking >> which is needed for memory management handling of protected virtual >> machines. It might also have some strange side effects for madvise >> MADV_DONTNEED and other things. >> >> We can simply try to get the userspace page set the bits and free the >> page. By storing the userspace address in the irq routing entry instead >> of the guest address we can actually avoid many lookups and list walks >> so that this variant is very likely not slower. >> >> If userspace messes around with the memory slots the worst thing that >> can happen is that we write to some other memory within that process. >> As we get the the page with FOLL_WRITE this can also not be used to >> write to shared read-only pages. >> >> Signed-off-by: Ulrich Weigand >> [borntraeger@de.ibm.com: patch simplification] >> Signed-off-by: Christian Borntraeger >> --- >> Documentation/virt/kvm/devices/s390_flic.rst | 11 +- >> arch/s390/include/asm/kvm_host.h | 3 - >> arch/s390/kvm/interrupt.c | 170 ++++++------------- >> 3 files changed, 53 insertions(+), 131 deletions(-) >> >> diff --git a/Documentation/virt/kvm/devices/s390_flic.rst b/Documentation/virt/kvm/devices/s390_flic.rst >> index 954190da7d04..ea96559ba501 100644 >> --- a/Documentation/virt/kvm/devices/s390_flic.rst >> +++ b/Documentation/virt/kvm/devices/s390_flic.rst >> @@ -108,16 +108,9 @@ Groups: >> mask or unmask the adapter, as specified in mask >> >> KVM_S390_IO_ADAPTER_MAP >> - perform a gmap translation for the guest address provided in addr, >> - pin a userspace page for the translated address and add it to the >> - list of mappings >> - >> - .. note:: A new mapping will be created unconditionally; therefore, >> - the calling code should avoid making duplicate mappings. >> - >> + This is now a no-op. The mapping is purely done by the irq route. >> KVM_S390_IO_ADAPTER_UNMAP >> - release a userspace page for the translated address specified in addr >> - from the list of mappings >> + This is now a no-op. The mapping is purely done by the irq route. >> > > The interface should have accepted a hva from the very start and not > guest addresses ... right, but that is history. > > [...] >> + /* >> + * We resolve the gpa to hva when setting the IRQ routing. the set_irq >> + * code uses get_user_pages_remote to do the actual write. > > nit: "get_user_pages_remote()" ack. > >> + */ >> case KVM_S390_IO_ADAPTER_MAP: >> - ret = kvm_s390_adapter_map(dev->kvm, req.id, req.addr); >> - break; >> case KVM_S390_IO_ADAPTER_UNMAP: >> - ret = kvm_s390_adapter_unmap(dev->kvm, req.id, req.addr); >> - break; >> + return 0; >> default: >> ret = -EINVAL; >> } >> @@ -2699,19 +2622,21 @@ static unsigned long get_ind_bit(__u64 addr, unsigned long bit_nr, bool swap) >> return swap ? (bit ^ (BITS_PER_LONG - 1)) : bit; >> } >> >> -static struct s390_map_info *get_map_info(struct s390_io_adapter *adapter, >> - u64 addr) >> +static struct page *get_map_page(struct kvm *kvm, >> + struct s390_io_adapter *adapter, >> + u64 uaddr) >> { >> - struct s390_map_info *map; >> + struct page *page = NULL; >> >> if (!adapter) >> return NULL; > > AFAIKs, this check is not necessary. Right otherwise we would crash earlier. > >> - >> - list_for_each_entry(map, &adapter->maps, list) { >> - if (map->guest_addr == addr) >> - return map; >> - } >> - return NULL; >> + if (!uaddr) >> + return NULL; > > I do wonder if that check is necessary. I don't think so but might be > missing something. Nothing should break when we remove this check. get_user_pages_remote will also return NULL (as newer kernels usually forbid mapping things at 0). Will remove. [...] >> @@ -2818,23 +2746,27 @@ int kvm_set_routing_entry(struct kvm *kvm, >> struct kvm_kernel_irq_routing_entry *e, >> const struct kvm_irq_routing_entry *ue) >> { >> - int ret; >> + u64 uaddr; >> >> switch (ue->type) { >> + /* we store the userspace addresses instead of the guest addresses */ >> case KVM_IRQ_ROUTING_S390_ADAPTER: >> e->set = set_adapter_int; >> - e->adapter.summary_addr = ue->u.adapter.summary_addr; >> - e->adapter.ind_addr = ue->u.adapter.ind_addr; >> + uaddr = gmap_translate(kvm->arch.gmap, ue->u.adapter.summary_addr); >> + if (uaddr == -EFAULT) >> + return -EFAULT; >> + e->adapter.summary_addr = uaddr; >> + uaddr = gmap_translate(kvm->arch.gmap, ue->u.adapter.ind_addr); >> + if (uaddr == -EFAULT) >> + return -EFAULT; > > AFAIK, leaving e->adapter.summary_addr set is not an issue. > > Interesting, in kvm_s390_adapter_map(), we didn't synchronize again slot > updates when doing the gmap_translate(), which looks wrong to me ... > > It seems to be the same thing here. I do wonder if it is safe to do a > gmap_translate() here, looks like this can race with > kvm_arch_commit_memory_region(). > > I would have assumed we need e.g., the slots_lock while doing the > gmap_translate() - or a srcu_read_lock(&vcpu->kvm->srcu) or similar ... gmap_translate does this via the gmap and it holds the mm sem. gmap_unmap_segment takes the same lock. So I think we are ok here. > > Apart from that, looks good to me. >