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mx.microsoft.com 1; spf=pass smtp.mailfrom=intel.com; dmarc=pass action=none header.from=intel.com; dkim=pass header.d=intel.com; arc=none Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=intel.com; Received: from DM3PR11MB8735.namprd11.prod.outlook.com (2603:10b6:0:4b::20) by SN7PR11MB7419.namprd11.prod.outlook.com (2603:10b6:806:34d::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8251.21; Wed, 18 Dec 2024 06:45:33 +0000 Received: from DM3PR11MB8735.namprd11.prod.outlook.com ([fe80::3225:d39b:ca64:ab95]) by DM3PR11MB8735.namprd11.prod.outlook.com ([fe80::3225:d39b:ca64:ab95%4]) with mapi id 15.20.8251.015; Wed, 18 Dec 2024 06:45:33 +0000 Message-ID: <7ee7534e-223f-4629-8523-622db551b66f@intel.com> Date: Wed, 18 Dec 2024 14:45:21 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/7] guest_memfd: Introduce an object to manage the guest-memfd with RamDiscardManager To: David Hildenbrand , Paolo Bonzini , Peter Xu , =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= , Michael Roth CC: , , Williams Dan J , Peng Chao P , Gao Chao , Xu Yilun References: <20241213070852.106092-1-chenyi.qiang@intel.com> <20241213070852.106092-3-chenyi.qiang@intel.com> From: Chenyi Qiang Content-Language: en-US In-Reply-To: <20241213070852.106092-3-chenyi.qiang@intel.com> Content-Type: text/plain; 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envelope-from=chenyi.qiang@intel.com; helo=mgamail.intel.com X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 12/13/2024 3:08 PM, Chenyi Qiang wrote: > As the commit 852f0048f3 ("RAMBlock: make guest_memfd require > uncoordinated discard") highlighted, some subsystems like VFIO might > disable ram block discard. However, guest_memfd relies on the discard > operation to perform page conversion between private and shared memory. > This can lead to stale IOMMU mapping issue when assigning a hardware > device to a confidential VM via shared memory (unprotected memory > pages). Blocking shared page discard can solve this problem, but it > could cause guests to consume twice the memory with VFIO, which is not > acceptable in some cases. An alternative solution is to convey other > systems like VFIO to refresh its outdated IOMMU mappings. > > RamDiscardManager is an existing concept (used by virtio-mem) to adjust > VFIO mappings in relation to VM page assignment. Effectively page > conversion is similar to hot-removing a page in one mode and adding it > back in the other, so the similar work that needs to happen in response > to virtio-mem changes needs to happen for page conversion events. > Introduce the RamDiscardManager to guest_memfd to achieve it. > > However, guest_memfd is not an object so it cannot directly implement > the RamDiscardManager interface. > > One solution is to implement the interface in HostMemoryBackend. Any > guest_memfd-backed host memory backend can register itself in the target > MemoryRegion. However, this solution doesn't cover the scenario where a > guest_memfd MemoryRegion doesn't belong to the HostMemoryBackend, e.g. > the virtual BIOS MemoryRegion. > > Thus, choose the second option, i.e. define an object type named > guest_memfd_manager with RamDiscardManager interface. Upon creation of > guest_memfd, a new guest_memfd_manager object can be instantiated and > registered to the managed guest_memfd MemoryRegion to handle the page > conversion events. > > In the context of guest_memfd, the discarded state signifies that the > page is private, while the populated state indicated that the page is > shared. The state of the memory is tracked at the granularity of the > host page size (i.e. block_size), as the minimum conversion size can be > one page per request. > > In addition, VFIO expects the DMA mapping for a specific iova to be > mapped and unmapped with the same granularity. However, the confidential > VMs may do partial conversion, e.g. conversion happens on a small region > within a large region. To prevent such invalid cases and before any > potential optimization comes out, all operations are performed with 4K > granularity. > > Signed-off-by: Chenyi Qiang > --- > include/sysemu/guest-memfd-manager.h | 46 +++++ > system/guest-memfd-manager.c | 250 +++++++++++++++++++++++++++ > system/meson.build | 1 + > 3 files changed, 297 insertions(+) > create mode 100644 include/sysemu/guest-memfd-manager.h > create mode 100644 system/guest-memfd-manager.c > > diff --git a/include/sysemu/guest-memfd-manager.h b/include/sysemu/guest-memfd-manager.h > new file mode 100644 > index 0000000000..ba4a99b614 > --- /dev/null > +++ b/include/sysemu/guest-memfd-manager.h > @@ -0,0 +1,46 @@ > +/* > + * QEMU guest memfd manager > + * > + * Copyright Intel > + * > + * Author: > + * Chenyi Qiang > + * > + * This work is licensed under the terms of the GNU GPL, version 2 or later. > + * See the COPYING file in the top-level directory > + * > + */ > + > +#ifndef SYSEMU_GUEST_MEMFD_MANAGER_H > +#define SYSEMU_GUEST_MEMFD_MANAGER_H > + > +#include "sysemu/hostmem.h" > + > +#define TYPE_GUEST_MEMFD_MANAGER "guest-memfd-manager" > + > +OBJECT_DECLARE_TYPE(GuestMemfdManager, GuestMemfdManagerClass, GUEST_MEMFD_MANAGER) > + > +struct GuestMemfdManager { > + Object parent; > + > + /* Managed memory region. */ > + MemoryRegion *mr; > + > + /* > + * 1-setting of the bit represents the memory is populated (shared). > + */ > + int32_t bitmap_size; > + unsigned long *bitmap; > + > + /* block size and alignment */ > + uint64_t block_size; > + > + /* listeners to notify on populate/discard activity. */ > + QLIST_HEAD(, RamDiscardListener) rdl_list; > +}; > + > +struct GuestMemfdManagerClass { > + ObjectClass parent_class; > +}; > + > +#endif > diff --git a/system/guest-memfd-manager.c b/system/guest-memfd-manager.c > new file mode 100644 > index 0000000000..d7e105fead > --- /dev/null > +++ b/system/guest-memfd-manager.c > @@ -0,0 +1,250 @@ > +/* > + * QEMU guest memfd manager > + * > + * Copyright Intel > + * > + * Author: > + * Chenyi Qiang > + * > + * This work is licensed under the terms of the GNU GPL, version 2 or later. > + * See the COPYING file in the top-level directory > + * > + */ > + > +#include "qemu/osdep.h" > +#include "qemu/error-report.h" > +#include "sysemu/guest-memfd-manager.h" > + > +OBJECT_DEFINE_SIMPLE_TYPE_WITH_INTERFACES(GuestMemfdManager, > + guest_memfd_manager, > + GUEST_MEMFD_MANAGER, > + OBJECT, > + { TYPE_RAM_DISCARD_MANAGER }, > + { }) > + Fixup: Use OBJECT_DEFINE_TYPE_WITH_INTERFACES() instead of OBJECT_DEFINE_SIMPLE_TYPE_WITH_INTERFACES() as we define a class struct. diff --git a/system/guest-memfd-manager.c b/system/guest-memfd-manager.c index 50802b34d7..f7dc93071a 100644 --- a/system/guest-memfd-manager.c +++ b/system/guest-memfd-manager.c @@ -15,12 +15,12 @@ #include "qemu/error-report.h" #include "sysemu/guest-memfd-manager.h" -OBJECT_DEFINE_SIMPLE_TYPE_WITH_INTERFACES(GuestMemfdManager, - guest_memfd_manager, - GUEST_MEMFD_MANAGER, - OBJECT, - { TYPE_RAM_DISCARD_MANAGER }, - { }) +OBJECT_DEFINE_TYPE_WITH_INTERFACES(GuestMemfdManager, + guest_memfd_manager, + GUEST_MEMFD_MANAGER, + OBJECT, + { TYPE_RAM_DISCARD_MANAGER }, + { }) static bool guest_memfd_rdm_is_populated(const RamDiscardManager *rdm,