From 19e8b596263c2ee966a4e45f0ffbc9bb08b55409 Mon Sep 17 00:00:00 2001 From: "Denis V. Lunev" Date: Fri, 19 Jun 2026 12:18:30 +0200 Subject: [PATCH] system/cpus: refuse memsave/pmemsave while guest RAM is being migrated MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit memsave and pmemsave read guest memory and write it to a file, with no guard at all. They run on the main thread with the BQL held, so on a postcopy destination touching a not-yet-received page deadlocks: the thread blocks on the userfault while the postcopy incoming path waits for the BQL to install that page. During precopy the read returns incomplete state instead. Refuse both while guest RAM is still being received, using the same migration_guest_ram_loading() check as dump-guest-memory. Signed-off-by: Denis V. Lunev Reviewed-by: Marc-André Lureau Message-Id: <20260619101834.228432-4-den@openvz.org> --- system/cpus.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/system/cpus.c b/system/cpus.c index 49f6daec3c..b31c825b46 100644 --- a/system/cpus.c +++ b/system/cpus.c @@ -43,6 +43,7 @@ #include "system/physmem.h" #include "system/replay.h" #include "system/runstate.h" +#include "migration/misc.h" #include "system/cpu-timers.h" #include "system/whpx.h" #include "hw/core/boards.h" @@ -843,6 +844,11 @@ void qmp_memsave(uint64_t addr, uint64_t size, const char *filename, uint8_t buf[1024]; uint64_t orig_addr = addr, orig_size = size; + if (migration_guest_ram_loading()) { + error_setg(errp, "Guest memory access not allowed during migration"); + return; + } + if (!has_cpu) { cpu_index = 0; } @@ -889,6 +895,11 @@ void qmp_pmemsave(uint64_t addr, uint64_t size, const char *filename, uint64_t l; uint8_t buf[1024]; + if (migration_guest_ram_loading()) { + error_setg(errp, "Guest memory access not allowed during migration"); + return; + } + f = fopen(filename, "wb"); if (!f) { error_setg_file_open(errp, errno, filename);