[libvirt PATCH 16/17] qemu: Wire up external limit manager

[Andrea Bolognani <abologna@xxxxxxxxxx>]

When the config knob is enabled, we simply skip the part where
limits are set; for the memory locking limit, which can change
dynamically over the lifetime of the guest, we still make sure
that the external process has set it correctly and error out
if that turns out not to be the case

This commit is better viewed with 'git show -w'.

https://bugzilla.redhat.com/show_bug.cgi?id=1916346

Signed-off-by: Andrea Bolognani <abologna@xxxxxxxxxx>
---
 src/conf/domain_conf.h  |  1 +
 src/qemu/qemu_domain.c  | 39 ++++++++++++++++++++++--------------
 src/qemu/qemu_process.c | 44 +++++++++++++++++++++++------------------
 3 files changed, 50 insertions(+), 34 deletions(-)

diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 7d208d881c..d1333020e1 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -2807,6 +2807,7 @@ struct _virDomainObj {
     size_t ndeprecations;
     char **deprecations;
 
+    bool externalLimitManager; /* Whether process limits are handled outside of libvirt */
     unsigned long long originalMemlock; /* Original RLIMIT_MEMLOCK, zero if no
                                          * restore will be required later */
 };
diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index f8b0e1a62a..0d9adb2f9c 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -9246,23 +9246,32 @@ qemuDomainAdjustMaxMemLock(virDomainObjPtr vm,
     if (virProcessGetMaxMemLock(vm->pid, &currentMemLock) < 0)
         return -1;
 
-    if (desiredMemLock > 0) {
-        /* If this is the first time adjusting the limit, save the current
-         * value so that we can restore it once memory locking is no longer
-         * required */
-        if (vm->originalMemlock == 0) {
-            vm->originalMemlock = currentMemLock;
+    if (!vm->externalLimitManager) {
+        if (desiredMemLock > 0) {
+            /* If this is the first time adjusting the limit, save the current
+             * value so that we can restore it once memory locking is no longer
+             * required */
+            if (vm->originalMemlock == 0) {
+                vm->originalMemlock = currentMemLock;
+            }
+        } else {
+            /* Once memory locking is no longer required, we can restore the
+             * original, usually very low, limit */
+            desiredMemLock = vm->originalMemlock;
+            vm->originalMemlock = 0;
         }
-    } else {
-        /* Once memory locking is no longer required, we can restore the
-         * original, usually very low, limit */
-        desiredMemLock = vm->originalMemlock;
-        vm->originalMemlock = 0;
-    }
 
-    if (desiredMemLock > 0 &&
-        virProcessSetMaxMemLock(vm->pid, desiredMemLock) < 0) {
-        return -1;
+        if (desiredMemLock > 0 &&
+            virProcessSetMaxMemLock(vm->pid, desiredMemLock) < 0) {
+            return -1;
+        }
+    } else {
+        if (currentMemLock < desiredMemLock) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("insufficient memlock limit (%llu < %llu)"),
+                           currentMemLock, desiredMemLock);
+            return -1;
+        }
     }
 
     return 0;
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index c05cbe3570..2eac3934c7 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -7016,25 +7016,31 @@ qemuProcessLaunch(virConnectPtr conn,
     virCommandSetPreExecHook(cmd, qemuProcessHook, &hookData);
     virCommandSetUmask(cmd, 0x002);
 
-    VIR_DEBUG("Setting up process limits");
-
-    /* In some situations, eg. VFIO passthrough, QEMU might need to lock a
-     * significant amount of memory, so we need to set the limit accordingly */
-    maxMemLock = qemuDomainGetMemLockLimitBytes(vm->def, false);
-
-    /* For all these settings, zero indicates that the limit should
-     * not be set explicitly and the default/inherited limit should
-     * be applied instead */
-    if (maxMemLock > 0)
-        virCommandSetMaxMemLock(cmd, maxMemLock);
-    if (cfg->maxProcesses > 0)
-        virCommandSetMaxProcesses(cmd, cfg->maxProcesses);
-    if (cfg->maxFiles > 0)
-        virCommandSetMaxFiles(cmd, cfg->maxFiles);
-
-    /* In this case, however, zero means that core dumps should be
-     * disabled, and so we always need to set the limit explicitly */
-    virCommandSetMaxCoreSize(cmd, cfg->maxCore);
+    if (cfg->externalLimitManager) {
+        VIR_DEBUG("Not setting up process limits (handled externally)");
+
+        vm->externalLimitManager = true;
+    } else {
+        VIR_DEBUG("Setting up process limits");
+
+        /* In some situations, eg. VFIO passthrough, QEMU might need to lock a
+         * significant amount of memory, so we need to set the limit accordingly */
+        maxMemLock = qemuDomainGetMemLockLimitBytes(vm->def, false);
+
+        /* For all these settings, zero indicates that the limit should
+         * not be set explicitly and the default/inherited limit should
+         * be applied instead */
+        if (maxMemLock > 0)
+            virCommandSetMaxMemLock(cmd, maxMemLock);
+        if (cfg->maxProcesses > 0)
+            virCommandSetMaxProcesses(cmd, cfg->maxProcesses);
+        if (cfg->maxFiles > 0)
+            virCommandSetMaxFiles(cmd, cfg->maxFiles);
+
+        /* In this case, however, zero means that core dumps should be
+         * disabled, and so we always need to set the limit explicitly */
+        virCommandSetMaxCoreSize(cmd, cfg->maxCore);
+    }
 
     VIR_DEBUG("Setting up security labelling");
     if (qemuSecuritySetChildProcessLabel(driver->securityManager,
-- 
2.26.2