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[99.254.114.190]) by smtp.gmail.com with ESMTPSA id ca18e2360f4ac-844737bc76dsm444189539f.5.2024.12.12.14.48.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Dec 2024 14:48:05 -0800 (PST) Date: Thu, 12 Dec 2024 17:48:03 -0500 From: Peter Xu To: Steven Sistare Cc: qemu-devel@nongnu.org, Fabiano Rosas , David Hildenbrand , Marcel Apfelbaum , Eduardo Habkost , Philippe Mathieu-Daude , Paolo Bonzini , "Daniel P. Berrange" , Markus Armbruster Subject: Re: [PATCH V4 06/19] physmem: preserve ram blocks for cpr Message-ID: References: <1733145611-62315-1-git-send-email-steven.sistare@oracle.com> <1733145611-62315-7-git-send-email-steven.sistare@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=170.10.133.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, DKIM_INVALID=0.1, DKIM_SIGNED=0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no 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 Thu, Dec 12, 2024 at 03:38:14PM -0500, Steven Sistare wrote: > On 12/9/2024 3:07 PM, Peter Xu wrote: > > On Mon, Dec 02, 2024 at 05:19:58AM -0800, Steve Sistare wrote: > > > Save the memfd for ramblocks in CPR state, along with a name that > > > uniquely identifies it. The block's idstr is not yet set, so it > > > cannot be used for this purpose. Find the saved memfd in new QEMU when > > > creating a block. If the block size is larger in new QEMU, extend the > > > block using fallocate, and the extra space will be useable after a guest > > > reset. > > > > > > Signed-off-by: Steve Sistare > > > --- > > > system/physmem.c | 36 ++++++++++++++++++++++++++++++++++-- > > > 1 file changed, 34 insertions(+), 2 deletions(-) > > > > > > diff --git a/system/physmem.c b/system/physmem.c > > > index 0bcb2cc..aa095a3 100644 > > > --- a/system/physmem.c > > > +++ b/system/physmem.c > > > @@ -70,6 +70,7 @@ > > > #include "qemu/pmem.h" > > > +#include "migration/cpr.h" > > > #include "migration/vmstate.h" > > > #include "qemu/range.h" > > > @@ -1661,6 +1662,19 @@ void qemu_ram_unset_idstr(RAMBlock *block) > > > } > > > } > > > +static char *cpr_name(RAMBlock *block) > > > +{ > > > + MemoryRegion *mr = block->mr; > > > + const char *mr_name = memory_region_name(mr); > > > + g_autofree char *id = mr->dev ? qdev_get_dev_path(mr->dev) : NULL; > > > + > > > + if (id) { > > > + return g_strdup_printf("%s/%s", id, mr_name); > > > + } else { > > > + return g_strdup(mr_name); > > > + } > > > +} > > > + > > > size_t qemu_ram_pagesize(RAMBlock *rb) > > > { > > > return rb->page_size; > > > @@ -2080,8 +2094,18 @@ 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; > > > + g_autofree char *name = cpr_name(new_block); > > > + int fd = cpr_find_fd(name, 0); > > > > If to use the proposed patch in the reply of patch 2, here this should be > > able to be moved to qemu_ram_alloc_anonymous_fd(), IIUC. > > > > > + > > > + if (fd >= 0) { > > > + if (lseek(fd, 0, SEEK_END) < max_length && ftruncate(fd, max_length)) { > > > + error_setg_errno(errp, errno, > > > + "cannot grow ram block %s fd %d to %ld bytes", > > > + name, fd, max_length); > > > + goto err; > > > + } > > > > I remember we discussed something similar to this, do we need ftruncate() > > at all? I think not. > > > > This happens when booting QEMU, so I don't think it's relevant yet to what > > size used in src, as this is dest. > > > > It starts to get relevant only when cpr migration starts on src, it sents > > ramblocks at the beginning, then parse_ramblock() will properly resize any > > ramblock to whatever size it should use. > > > > If the resize didn't happen it can only mean that used_length is correctly > > matched on both sides. > > > > So I don't see why a special truncate() call is needed yet.. > > You suggested truncate: > > https://lore.kernel.org/qemu-devel/47d6d984-7002-4086-bb10-b191168f141f@oracle.com/ > > "So after such system reset, QEMU might start to see new ROM code loaded > here (not the one that got migrated anymore, which will only match the > version installed on src QEMU). Here the problem is the new firmware can > be larger, so I _think_ we need to make sure max_length is not modified by > CPR to allow resizing happen here, while if we use truncate=true here it > should just work in all cases." > > ... but you suggested passing a truncate bool to the file_ram_alloc call after > cpr_find_fd. I could do that instead. However, if qemu_ram_alloc_shared uses > qemu_ram_alloc_from_fd instead of file_ram_alloc, per your suggestion in patch 2, > then I will still call ftruncate here, because qemu_ram_alloc_from_fd does not > take a truncate argument. My memory was when reuse qemu_ram_alloc_from_fd() in that suggestion of patch 2, it will only create zero-length fd (with fsize=0) and leave all the rest to qemu_ram_alloc_from_fd(), then with that: qemu_ram_alloc_from_fd: new_block->host = file_ram_alloc(new_block, size, fd, !file_size, offset, errp); So that'll always have truncate==!file_size==1. Then truncate will be done at file_ram_alloc() later, iiuc. if (truncate && ftruncate(fd, offset + memory)) { perror("ftruncate"); } Would this work? Meanwhile, this whole ram resize discussion reminded me that to reuse qemu_ram_alloc_from_fd(), we may also want to make sure to pass ->resized() hook from qemu_ram_alloc_internal() to the fd helper too.. IOW, we may want to keep qemu_ram_resize() invoke those hooks, even after switching to fd-based for aux mems. Maybe the size / max_size also need to be passed over? As for fd ramblock it used to be always the same on used_length/max_length, but not anymore when we switch aux mem to fd based. Please feel free to double check.. -- Peter Xu