Re: [libvirt] [PATCH v3] qemu: Add check for whether KVM nesting is enabled

Support for nested KVM is handled via a kernel module configuration parameters values for kvm_intel, kvm_amd, kvm_hv (PPC), or kvm (s390). While it's possible to fetch the kmod config values via virKModConfig, unfortunately that is the static value and we need to get the current/dynamic value from the kernel file system. So this patch adds a new API virHostKVMSupportsNesting that will search the 3 kernel modules to get the nesting value and check if it is 'Y' (or 'y' just in case) or '1' to return a true/false whether the KVM kernel supports nesting. We need to do this in order to handle cases where adjustments to the value are made after libvirtd is started to force a refetch of the latest QEMU capabilities since the correct CPU settings need to be made for a guest to add the "vmx=on" to/for the guest config. Signed-off-by: John Ferlan <jferlan(a)redhat.com&gt; NB to be removed before push - I got data from: (IBM Z) https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/... (PPC slide 131) https://events.linuxfoundation.org/wp-content/uploads/2017/12/Taking-it-t... Signed-off-by: John Ferlan <jferlan(a)redhat.com&gt; --- v2: https://www.redhat.com/archives/libvir-list/2018-November/msg00955.html Changes from code review... - Rename variables/API's to KVMSupportsNested - Movement of logic to check/set the 'nested' to inside locations that ensure KVM was enabled (via capability). - Change of logic to not use virKModConfig and instead look at the running kernel value for /sys/module/*/parameters/nested where * is kvm_intel, kvm_amd, kvm_hv, or kvm src/qemu/qemu_capabilities.c | 54 ++++++++++++++++++++++++++++++++++++ 1 file changed, 54 insertions(+) diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c index 20a1a0c201..bef92a679f 100644 --- a/src/qemu/qemu_capabilities.c +++ b/src/qemu/qemu_capabilities.c @@ -558,6 +558,7 @@ struct _virQEMUCaps { virObject parent; bool usedQMP; + bool kvmSupportsNesting; char *binary; time_t ctime; @@ -1530,6 +1531,7 @@ virQEMUCapsPtr virQEMUCapsNewCopy(virQEMUCapsPtr qemuCaps) return NULL; ret->usedQMP = qemuCaps->usedQMP; + ret->kvmSupportsNesting = qemuCaps->kvmSupportsNesting; if (VIR_STRDUP(ret->binary, qemuCaps->binary) < 0) goto error; @@ -3589,6 +3591,9 @@ virQEMUCapsLoadCache(virArch hostArch, virQEMUCapsInitHostCPUModel(qemuCaps, hostArch, VIR_DOMAIN_VIRT_KVM); virQEMUCapsInitHostCPUModel(qemuCaps, hostArch, VIR_DOMAIN_VIRT_QEMU); + if (virXPathBoolean("boolean(./kvmSupportsNesting)", ctxt) > 0) + qemuCaps->kvmSupportsNesting = true; + ret = 0; cleanup: VIR_FREE(str); @@ -3808,6 +3813,9 @@ virQEMUCapsFormatCache(virQEMUCapsPtr qemuCaps) if (qemuCaps->sevCapabilities) virQEMUCapsFormatSEVInfo(qemuCaps, &buf); + if (qemuCaps->kvmSupportsNesting) + virBufferAddLit(&buf, "<kvmSupportsNesting/>\n"); + virBufferAdjustIndent(&buf, -2); virBufferAddLit(&buf, "</qemuCaps>\n"); @@ -3848,6 +3856,41 @@ virQEMUCapsSaveFile(void *data, } +/* Check the kernel module parameters 'nested' file to determine if enabled + * + * Intel: 'kvm_intel' uses 'Y' + * AMD: 'kvm_amd' uses '1' + * PPC64: 'kvm_hv' uses 'Y' + * S390: 'kvm' uses '1' + */ +static bool +virQEMUCapsKVMSupportsNesting(void) +{ + static char const * const kmod[] = {"kvm_intel", "kvm_amd", + "kvm_hv", "kvm"}; + VIR_AUTOFREE(char *) value = NULL; + int rc; + size_t i; + + for (i = 0; i < ARRAY_CARDINALITY(kmod); i++) { + VIR_FREE(value); + rc = virFileReadValueString(&value, "/sys/module/%s/parameters/nested", + kmod[i]); + if (rc == -2) + continue; + if (rc < 0) { + virResetLastError(); + return false; + } + + if (value[0] == 'Y' || value[0] == 'y' || value[0] == '1') + return true; + } + + return false; +} + + static bool virQEMUCapsIsValid(void *data, void *privData) @@ -3856,6 +3899,7 @@ virQEMUCapsIsValid(void *data, virQEMUCapsCachePrivPtr priv = privData; bool kvmUsable; struct stat sb; + bool kvmSupportsNesting; if (!qemuCaps->binary) return true; @@ -3933,6 +3977,14 @@ virQEMUCapsIsValid(void *data, qemuCaps->kernelVersion); return false; } + + kvmSupportsNesting = virQEMUCapsKVMSupportsNesting(); + if (kvmSupportsNesting != qemuCaps->kvmSupportsNesting) { + VIR_DEBUG("Outdated capabilities for '%s': kvm kernel nested " + "value changed from %d", + qemuCaps->binary, qemuCaps->kvmSupportsNesting); + return false; + } } return true; @@ -4576,6 +4628,8 @@ virQEMUCapsNewForBinaryInternal(virArch hostArch, if (VIR_STRDUP(qemuCaps->kernelVersion, kernelVersion) < 0) goto error; + + qemuCaps->kvmSupportsNesting = virQEMUCapsKVMSupportsNesting(); } cleanup: