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Mon, 10 Feb 2020 12:26:58 +0000 (UTC) Received: from [10.36.117.242] (ovpn-117-242.ams2.redhat.com [10.36.117.242]) by smtp.corp.redhat.com (Postfix) with ESMTP id B213410013A7; Mon, 10 Feb 2020 12:26:55 +0000 (UTC) Subject: Re: [PATCH 02/35] KVM: s390/interrupt: do not pin adapter interrupt pages To: Christian Borntraeger , Janosch Frank Cc: KVM , Cornelia Huck , Thomas Huth , Ulrich Weigand , Claudio Imbrenda , Andrea Arcangeli , linux-s390 , Michael Mueller , Vasily Gorbik , linux-mm@kvack.org, Andrew Morton References: <20200207113958.7320-1-borntraeger@de.ibm.com> <20200207113958.7320-3-borntraeger@de.ibm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: <2cf62b84-8eb6-18d5-437b-7e86401b9c45@redhat.com> Date: Mon, 10 Feb 2020 13:26:54 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200207113958.7320-3-borntraeger@de.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 07.02.20 12:39, Christian Borntraeger wrote: > From: Ulrich Weigand >=20 > 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. > We can reuse the pte notifiers to "cache" the page without pinning it. >=20 > Signed-off-by: Ulrich Weigand > Suggested-by: Andrea Arcangeli > [borntraeger@de.ibm.com: patch merging, splitting, fixing] > Signed-off-by: Christian Borntraeger > --- So, instead of pinning explicitly, look up the page address, cache it, and glue its lifetime to the gmap table entry. When that entry is changed, invalidate the cached page. On re-access, look up the page again and register the gmap notifier for the table entry again. [...] > #define MAX_S390_IO_ADAPTERS ((MAX_ISC + 1) * 8) > diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c > index c06c89d370a7..4bfb2f8fe57c 100644 > --- a/arch/s390/kvm/interrupt.c > +++ b/arch/s390/kvm/interrupt.c > @@ -28,6 +28,7 @@ > #include > #include > #include > +#include > #include "kvm-s390.h" > #include "gaccess.h" > #include "trace-s390.h" > @@ -2328,8 +2329,8 @@ static int register_io_adapter(struct kvm_device = *dev, > return -ENOMEM; > =20 > INIT_LIST_HEAD(&adapter->maps); > - init_rwsem(&adapter->maps_lock); > - atomic_set(&adapter->nr_maps, 0); > + spin_lock_init(&adapter->maps_lock); > + adapter->nr_maps =3D 0; > adapter->id =3D adapter_info.id; > adapter->isc =3D adapter_info.isc; > adapter->maskable =3D adapter_info.maskable; > @@ -2375,19 +2376,15 @@ static int kvm_s390_adapter_map(struct kvm *kvm= , unsigned int id, __u64 addr) > ret =3D -EFAULT; > goto out; > } > - ret =3D get_user_pages_fast(map->addr, 1, FOLL_WRITE, &map->page); > - if (ret < 0) > - goto out; > - BUG_ON(ret !=3D 1); > - down_write(&adapter->maps_lock); > - if (atomic_inc_return(&adapter->nr_maps) < MAX_S390_ADAPTER_MAPS) { > + spin_lock(&adapter->maps_lock); > + if (adapter->nr_maps < MAX_S390_ADAPTER_MAPS) { > + adapter->nr_maps++; > list_add_tail(&map->list, &adapter->maps); I do wonder if we should check for duplicates. The unmap path will only remove exactly one entry. But maybe this can never happen or is already handled on a a higher layer. > } > @@ -2430,7 +2426,6 @@ void kvm_s390_destroy_adapters(struct kvm *kvm) > list_for_each_entry_safe(map, tmp, > &kvm->arch.adapters[i]->maps, list) { > list_del(&map->list); > - put_page(map->page); > kfree(map); > } > kfree(kvm->arch.adapters[i]); Between the gmap being removed in kvm_arch_vcpu_destroy() and kvm_s390_destroy_adapters(), the entries would no longer properly get invalidated. AFAIK, removing/freeing the gmap will not trigger any notifiers. Not sure if that's an issue (IOW, if we can have some very weird race). But I guess we would have similar races already :) > @@ -2690,6 +2685,31 @@ struct kvm_device_ops kvm_flic_ops =3D { > .destroy =3D flic_destroy, > }; > =20 > +void kvm_s390_adapter_gmap_notifier(struct gmap *gmap, unsigned long s= tart, > + unsigned long end) > +{ > + struct kvm *kvm =3D gmap->private; > + struct s390_map_info *map, *tmp; > + int i; > + > + for (i =3D 0; i < MAX_S390_IO_ADAPTERS; i++) { > + struct s390_io_adapter *adapter =3D kvm->arch.adapters[i]; > + > + if (!adapter) > + continue; I have to ask very dumb: How is kvm->arch.adapters[] protected? I don't see any explicit locking e.g., on flic_set_attr()->register_io_adapter(). [...]> +static struct page *get_map_page(struct kvm *kvm, > + struct s390_io_adapter *adapter, > + u64 addr) > { > struct s390_map_info *map; > + unsigned long uaddr; > + struct page *page; > + bool need_retry; > + int ret; > =20 > if (!adapter) > return NULL; > +retry: > + page =3D NULL; > + uaddr =3D 0; > + spin_lock(&adapter->maps_lock); > + list_for_each_entry(map, &adapter->maps, list) > + if (map->guest_addr =3D=3D addr) { Could it happen, that we don't have a fitting entry in the list? > + uaddr =3D map->addr; > + page =3D map->page; > + if (!page) > + map->page =3D ERR_PTR(-EBUSY); > + else if (IS_ERR(page) || !page_cache_get_speculative(page)) { > + spin_unlock(&adapter->maps_lock); > + goto retry; > + } > + break; > + } Can we please factor out looking up the list entry to a separate function, to be called under lock? (and e.g., use it below as well) spin_lock(&adapter->maps_lock); entry =3D fancy_new_function(); if (!entry) return NULL; uaddr =3D entry->addr; page =3D entry->page; if (!page) ... spin_unlock(&adapter->maps_lock); > + spin_unlock(&adapter->maps_lock); > + > + if (page) > + return page; > + if (!uaddr) > + return NULL; > =20 > - list_for_each_entry(map, &adapter->maps, list) { > - if (map->guest_addr =3D=3D addr) > - return map; > + down_read(&kvm->mm->mmap_sem); > + ret =3D set_pgste_bits(kvm->mm, uaddr, PGSTE_IN_BIT, PGSTE_IN_BIT); > + if (ret) > + goto fail; > + ret =3D get_user_pages_remote(NULL, kvm->mm, uaddr, 1, FOLL_WRITE, > + &page, NULL, NULL); > + if (ret < 1) > + page =3D NULL; > +fail: > + up_read(&kvm->mm->mmap_sem); > + need_retry =3D true; > + spin_lock(&adapter->maps_lock); > + list_for_each_entry(map, &adapter->maps, list) > + if (map->guest_addr =3D=3D addr) { Could it happen that our entry is suddenly no longer in the list? > + if (map->page =3D=3D ERR_PTR(-EBUSY)) { > + map->page =3D page; > + need_retry =3D false; > + } else if (IS_ERR(map->page)) { else if (map->page =3D=3D ERR_PTR(-EINVAL) or simpy "else" (every other value would be a BUG_ON, right?) /* race with a notifier - don't store the entry and retry */ > + map->page =3D NULL;> + } > + break; > + } > + spin_unlock(&adapter->maps_lock); > + if (need_retry) { > + if (page) > + put_page(page); > + goto retry; > } > - return NULL; > + > + return page; Wow, this function is ... special. Took me way to long to figure out what is going on here. We certainly need comments in there. I can see that - ERR_PTR(-EBUSY) is used when somebody is about to do the get_user_pages_remote(). others have to loop until that is resolved. - ERR_PTR(-EINVAL) is used when the entry gets invalidated by the notifier while somebody is about to set it (while still ERR_PTR(-EBUSY)). The one currently processing the entry will eventually set it back to NULL. I think we should make this clearer by only setting ERR_PTR(-EINVAL) in the notifier if already ERR_PTR(-EBUSY), along with a comment. Can we document the values for map->page and how they are to be handled right in the struct? --=20 Thanks, David / dhildenb