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Berrange" , Markus Armbruster , Steve Sistare Subject: [PATCH V4 02/19] physmem: fd-based shared memory Date: Mon, 2 Dec 2024 05:19:54 -0800 Message-Id: <1733145611-62315-3-git-send-email-steven.sistare@oracle.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1733145611-62315-1-git-send-email-steven.sistare@oracle.com> References: <1733145611-62315-1-git-send-email-steven.sistare@oracle.com> X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2024-12-02_09,2024-12-02_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 mlxlogscore=999 spamscore=0 suspectscore=0 malwarescore=0 mlxscore=0 phishscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2411120000 definitions=main-2412020116 X-Proofpoint-ORIG-GUID: _grpuIs03P-XbjUKAO7KEPnM8ztbpaEw X-Proofpoint-GUID: _grpuIs03P-XbjUKAO7KEPnM8ztbpaEw Received-SPF: pass client-ip=205.220.177.32; envelope-from=steven.sistare@oracle.com; helo=mx0b-00069f02.pphosted.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_MED=-0.444, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, 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 Create MAP_SHARED RAMBlocks by mmap'ing a file descriptor rather than using MAP_ANON, so the memory can be accessed in another process by passing and mmap'ing the fd. This will allow CPR to support memory-backend-ram and memory-backend-shm objects, provided the user creates them with share=on. Use memfd_create if available because it has no constraints. If not, use POSIX shm_open. However, this may fail if the shm mount size is too small, even if the system has free memory, so for backwards compatibility fall back to qemu_anon_ram_alloc/MAP_ANON on shm_open failure. For backwards compatibility on Windows, always use MAP_ANON. share=on has no purpose there, but the syntax is accepted, and must continue to work. Exclude Xen. Xen ignores RAM_SHARED and does its own allocation. Signed-off-by: Steve Sistare --- system/physmem.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++---- system/trace-events | 1 + 2 files changed, 81 insertions(+), 5 deletions(-) diff --git a/system/physmem.c b/system/physmem.c index dc1db3a..b0c4b22 100644 --- a/system/physmem.c +++ b/system/physmem.c @@ -47,6 +47,7 @@ #include "qemu/qemu-print.h" #include "qemu/log.h" #include "qemu/memalign.h" +#include "qemu/memfd.h" #include "exec/memory.h" #include "exec/ioport.h" #include "sysemu/dma.h" @@ -2057,6 +2058,70 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr, } #endif +static bool qemu_memfd_available(void) +{ + static int has_memfd = -1; + + if (has_memfd < 0) { + has_memfd = qemu_memfd_check(0); + } + return has_memfd; +} + +/* + * We want anonymous shared memory, similar to MAP_SHARED|MAP_ANON, but + * some users want the fd. Allocate shm explicitly to get an fd. + */ +static bool qemu_ram_alloc_shared(RAMBlock *new_block, Error **errp) +{ + size_t max_length = new_block->max_length; + MemoryRegion *mr = new_block->mr; + const char *name = memory_region_name(mr); + int fd; + + if (qemu_memfd_available()) { + fd = qemu_memfd_create(name, max_length + mr->align, 0, 0, 0, errp); + if (fd < 0) { + return false; + } + } else if (!qemu_shm_available()) { + /* + * Backwards compatibility for Windows. The user may specify a + * memory backend with shared=on, and Windows ignores shared. + * Fall back to qemu_anon_ram_alloc. + */ + return true; + } else { + Error *local_err = NULL; + + fd = qemu_shm_alloc(max_length, &local_err); + if (fd < 0) { + /* + * Backwards compatibility in case the shm mount size is too small. + * Previous QEMU versions called qemu_anon_ram_alloc for anonymous + * shared memory, which could succeed. + */ + error_prepend(&local_err, + "Retrying using MAP_ANON|MAP_SHARED because: "); + warn_report_err(local_err); + return true; + } + } + + new_block->mr->align = QEMU_VMALLOC_ALIGN; + new_block->host = file_ram_alloc(new_block, max_length, fd, false, 0, errp); + + if (new_block->host) { + qemu_set_cloexec(fd); + new_block->fd = fd; + trace_qemu_ram_alloc_shared(name, max_length, fd, new_block->host); + return true; + } + + close(fd); + return false; +} + static RAMBlock *qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size, void (*resized)(const char*, @@ -2089,13 +2154,23 @@ RAMBlock *qemu_ram_alloc_internal(ram_addr_t size, ram_addr_t max_size, new_block->page_size = qemu_real_host_page_size(); new_block->host = host; new_block->flags = ram_flags; + + if (!host && !xen_enabled()) { + if ((new_block->flags & RAM_SHARED) && + !qemu_ram_alloc_shared(new_block, &local_err)) { + goto err; + } + } + ram_block_add(new_block, &local_err); - if (local_err) { - g_free(new_block); - error_propagate(errp, local_err); - return NULL; + if (!local_err) { + return new_block; } - return new_block; + +err: + g_free(new_block); + error_propagate(errp, local_err); + return NULL; } RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host, diff --git a/system/trace-events b/system/trace-events index 5bbc3fb..831a60c 100644 --- a/system/trace-events +++ b/system/trace-events @@ -33,6 +33,7 @@ address_space_map(void *as, uint64_t addr, uint64_t len, bool is_write, uint32_t find_ram_offset(uint64_t size, uint64_t offset) "size: 0x%" PRIx64 " @ 0x%" PRIx64 find_ram_offset_loop(uint64_t size, uint64_t candidate, uint64_t offset, uint64_t next, uint64_t mingap) "trying size: 0x%" PRIx64 " @ 0x%" PRIx64 ", offset: 0x%" PRIx64" next: 0x%" PRIx64 " mingap: 0x%" PRIx64 ram_block_discard_range(const char *rbname, void *hva, size_t length, bool need_madvise, bool need_fallocate, int ret) "%s@%p + 0x%zx: madvise: %d fallocate: %d ret: %d" +qemu_ram_alloc_shared(const char *name, size_t max_length, int fd, void *host) "%s size %zu fd %d host %p" # cpus.c vm_stop_flush_all(int ret) "ret %d"