The KVM_CHECK_EXTENSION ioctl can be issued either on the global fd
(/dev/kvm), or on the VM fd obtained with KVM_CREATE_VM. For most
extensions, KVM returns the same value with either method, but for some
of them it can refine the returned value depending on the VM type. The
KVM documentation [1] advises to use the VM fd:
Based on their initialization different VMs may have different
capabilities. It is thus encouraged to use the vm ioctl to query for
capabilities (available with KVM_CAP_CHECK_EXTENSION_VM on the vm fd)
Ongoing work on Arm confidential VMs confirms this, as some capabilities
become unavailable to confidential VMs, requiring changes in QEMU to use
kvm_vm_check_extension() instead of kvm_check_extension() [2]. Rather
than changing each check one by one, change kvm_check_extension() to
always issue the ioctl on the VM fd when available, and remove
kvm_vm_check_extension().
Fall back to the global fd when the VM check is unavailable:
* Ancient kernels do not support KVM_CHECK_EXTENSION on the VM fd, since
it was added by commit 92b591a4c46b ("KVM: Allow KVM_CHECK_EXTENSION
on the vm fd") in Linux 3.17 [3]. Support for Linux 3.16 ended only in
June 2020, but there may still be old images around.
* A couple of calls must be issued before the VM fd is available, since
they determine the VM type: KVM_CAP_MIPS_VZ and KVM_CAP_ARM_VM_IPA_SIZE
Does any user actually depend on the check being done on the global fd
instead of the VM fd? I surveyed all cases where KVM can return
different values depending on the query method. Luckily QEMU already
calls kvm_vm_check_extension() for most of those. Only three of them are
ambiguous, because currently done on the global fd:
* KVM_CAP_MAX_VCPUS and KVM_CAP_MAX_VCPU_ID on Arm, changes value if the
user requests a vGIC different from the default. But QEMU queries this
before vGIC configuration, so the reported value will be the same.
* KVM_CAP_SW_TLB on PPC. When issued on the global fd, returns false if
the kvm-hv module is loaded; when issued on the VM fd, returns false
only if the VM type is HV instead of PR. If this returns false, then
QEMU will fail to initialize a BOOKE206 MMU model.
So this patch supposedly improves things, as it allows to run this
type of vCPU even when both KVM modules are loaded.
* KVM_CAP_PPC_SECURE_GUEST. Similarly, doing this check on a VM fd
refines the returned value, and ensures that SVM is actually
supported. Since QEMU follows the check with kvm_vm_enable_cap(), this
patch should only provide better error reporting.
[1] https://www.kernel.org/doc/html/latest/virt/kvm/api.html#kvm-check-extension
[2] https://lore.kernel.org/kvm/875ybi0ytc.fsf@xxxxxxxxxx/
[3] https://github.com/torvalds/linux/commit/92b591a4c46b
Suggested-by: Cornelia Huck <cohuck@xxxxxxxxxx>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
---
include/sysemu/kvm.h | 2 --
include/sysemu/kvm_int.h | 1 +
accel/kvm/kvm-all.c | 26 +++++++++-----------------
target/i386/kvm/kvm.c | 6 +++---
target/ppc/kvm.c | 34 +++++++++++++++++-----------------
5 files changed, 30 insertions(+), 39 deletions(-)
diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
index c8281c07a7..d62054004e 100644
--- a/include/sysemu/kvm.h
+++ b/include/sysemu/kvm.h
@@ -438,8 +438,6 @@ bool kvm_arch_stop_on_emulation_error(CPUState *cpu);
int kvm_check_extension(KVMState *s, unsigned int extension);
-int kvm_vm_check_extension(KVMState *s, unsigned int extension);
-
#define kvm_vm_enable_cap(s, capability, cap_flags, ...) \
({ \
struct kvm_enable_cap cap = { \
diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h
index a641c974ea..f6aa22ea09 100644
--- a/include/sysemu/kvm_int.h
+++ b/include/sysemu/kvm_int.h
@@ -122,6 +122,7 @@ struct KVMState
uint32_t xen_caps;
uint16_t xen_gnttab_max_frames;
uint16_t xen_evtchn_max_pirq;
+ bool check_extension_vm;
};
void kvm_memory_listener_register(KVMState *s, KVMMemoryListener *kml,
diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index cf3a88d90e..eca815e763 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -1109,22 +1109,13 @@ int kvm_check_extension(KVMState *s, unsigned int extension)
{
int ret;
- ret = kvm_ioctl(s, KVM_CHECK_EXTENSION, extension);
- if (ret < 0) {
- ret = 0;
+ if (!s->check_extension_vm) {
+ ret = kvm_ioctl(s, KVM_CHECK_EXTENSION, extension);
+ } else {
+ ret = kvm_vm_ioctl(s, KVM_CHECK_EXTENSION, extension);
}
-
- return ret;
-}
-
-int kvm_vm_check_extension(KVMState *s, unsigned int extension)
-{
- int ret;
-
- ret = kvm_vm_ioctl(s, KVM_CHECK_EXTENSION, extension);
if (ret < 0) {
- /* VM wide version not implemented, use global one instead */
- ret = kvm_check_extension(s, extension);
+ ret = 0;
}
return ret;
@@ -2328,7 +2319,7 @@ static void kvm_irqchip_create(KVMState *s)
*/
static int kvm_recommended_vcpus(KVMState *s)
{
- int ret = kvm_vm_check_extension(s, KVM_CAP_NR_VCPUS);
+ int ret = kvm_check_extension(s, KVM_CAP_NR_VCPUS);
return (ret) ? ret : 4;
}
@@ -2480,6 +2471,7 @@ static int kvm_init(MachineState *ms)
}
s->vmfd = ret;
+ s->check_extension_vm = kvm_check_extension(s, KVM_CAP_CHECK_EXTENSION_VM);
/* check the vcpu limits */
soft_vcpus_limit = kvm_recommended_vcpus(s);
@@ -2527,7 +2519,7 @@ static int kvm_init(MachineState *ms)
ring_bytes = s->kvm_dirty_ring_size * sizeof(struct kvm_dirty_gfn);
/* Read the max supported pages */
- ret = kvm_vm_check_extension(s, KVM_CAP_DIRTY_LOG_RING);
+ ret = kvm_check_extension(s, KVM_CAP_DIRTY_LOG_RING);
if (ret > 0) {
if (ring_bytes > ret) {
error_report("KVM dirty ring size %" PRIu32 " too big "
@@ -2680,7 +2672,7 @@ static int kvm_init(MachineState *ms)
s->many_ioeventfds = kvm_check_many_ioeventfds();
- s->sync_mmu = !!kvm_vm_check_extension(kvm_state, KVM_CAP_SYNC_MMU);
+ s->sync_mmu = !!kvm_check_extension(kvm_state, KVM_CAP_SYNC_MMU);
if (!s->sync_mmu) {
ret = ram_block_discard_disable(true);
assert(!ret);
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index de531842f6..14f0164fe6 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -161,7 +161,7 @@ int kvm_has_pit_state2(void)
bool kvm_has_smm(void)
{
- return kvm_vm_check_extension(kvm_state, KVM_CAP_X86_SMM);
+ return kvm_check_extension(kvm_state, KVM_CAP_X86_SMM);
}
bool kvm_has_adjust_clock_stable(void)
@@ -2747,7 +2747,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
return ret;
}
}
- if (kvm_vm_check_extension(s, KVM_CAP_X86_USER_SPACE_MSR)) {
+ if (kvm_check_extension(s, KVM_CAP_X86_USER_SPACE_MSR)) {
bool r;
ret = kvm_vm_enable_cap(s, KVM_CAP_X86_USER_SPACE_MSR, 0,
@@ -5403,7 +5403,7 @@ static bool __kvm_enable_sgx_provisioning(KVMState *s)
{
int fd, ret;
- if (!kvm_vm_check_extension(s, KVM_CAP_SGX_ATTRIBUTE)) {
+ if (!kvm_check_extension(s, KVM_CAP_SGX_ATTRIBUTE)) {
return false;
}
diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 78f6fc50cd..055a8acdcd 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -100,7 +100,7 @@ static uint32_t debug_inst_opcode;
static bool kvmppc_is_pr(KVMState *ks)
{
/* Assume KVM-PR if the GET_PVINFO capability is available */
- return kvm_vm_check_extension(ks, KVM_CAP_PPC_GET_PVINFO) != 0;
+ return kvm_check_extension(ks, KVM_CAP_PPC_GET_PVINFO) != 0;
}
static int kvm_ppc_register_host_cpu_type(void);
@@ -112,11 +112,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
cap_interrupt_unset = kvm_check_extension(s, KVM_CAP_PPC_UNSET_IRQ);
cap_segstate = kvm_check_extension(s, KVM_CAP_PPC_SEGSTATE);
cap_booke_sregs = kvm_check_extension(s, KVM_CAP_PPC_BOOKE_SREGS);
- cap_ppc_smt_possible = kvm_vm_check_extension(s, KVM_CAP_PPC_SMT_POSSIBLE);
+ cap_ppc_smt_possible = kvm_check_extension(s, KVM_CAP_PPC_SMT_POSSIBLE);
cap_spapr_tce = kvm_check_extension(s, KVM_CAP_SPAPR_TCE);
cap_spapr_tce_64 = kvm_check_extension(s, KVM_CAP_SPAPR_TCE_64);
cap_spapr_multitce = kvm_check_extension(s, KVM_CAP_SPAPR_MULTITCE);
- cap_spapr_vfio = kvm_vm_check_extension(s, KVM_CAP_SPAPR_TCE_VFIO);
+ cap_spapr_vfio = kvm_check_extension(s, KVM_CAP_SPAPR_TCE_VFIO);
cap_one_reg = kvm_check_extension(s, KVM_CAP_ONE_REG);
cap_hior = kvm_check_extension(s, KVM_CAP_PPC_HIOR);
cap_epr = kvm_check_extension(s, KVM_CAP_PPC_EPR);
@@ -125,23 +125,23 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
* Note: we don't set cap_papr here, because this capability is
* only activated after this by kvmppc_set_papr()
*/
- cap_htab_fd = kvm_vm_check_extension(s, KVM_CAP_PPC_HTAB_FD);
+ cap_htab_fd = kvm_check_extension(s, KVM_CAP_PPC_HTAB_FD);
cap_fixup_hcalls = kvm_check_extension(s, KVM_CAP_PPC_FIXUP_HCALL);
- cap_ppc_smt = kvm_vm_check_extension(s, KVM_CAP_PPC_SMT);
- cap_htm = kvm_vm_check_extension(s, KVM_CAP_PPC_HTM);
- cap_mmu_radix = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_RADIX);
- cap_mmu_hash_v3 = kvm_vm_check_extension(s, KVM_CAP_PPC_MMU_HASH_V3);
- cap_xive = kvm_vm_check_extension(s, KVM_CAP_PPC_IRQ_XIVE);
- cap_resize_hpt = kvm_vm_check_extension(s, KVM_CAP_SPAPR_RESIZE_HPT);
+ cap_ppc_smt = kvm_check_extension(s, KVM_CAP_PPC_SMT);
+ cap_htm = kvm_check_extension(s, KVM_CAP_PPC_HTM);
+ cap_mmu_radix = kvm_check_extension(s, KVM_CAP_PPC_MMU_RADIX);
+ cap_mmu_hash_v3 = kvm_check_extension(s, KVM_CAP_PPC_MMU_HASH_V3);
+ cap_xive = kvm_check_extension(s, KVM_CAP_PPC_IRQ_XIVE);
+ cap_resize_hpt = kvm_check_extension(s, KVM_CAP_SPAPR_RESIZE_HPT);
kvmppc_get_cpu_characteristics(s);
- cap_ppc_nested_kvm_hv = kvm_vm_check_extension(s, KVM_CAP_PPC_NESTED_HV);
+ cap_ppc_nested_kvm_hv = kvm_check_extension(s, KVM_CAP_PPC_NESTED_HV);
cap_large_decr = kvmppc_get_dec_bits();
- cap_fwnmi = kvm_vm_check_extension(s, KVM_CAP_PPC_FWNMI);
+ cap_fwnmi = kvm_check_extension(s, KVM_CAP_PPC_FWNMI);
/*
* Note: setting it to false because there is not such capability
* in KVM at this moment.
*
- * TODO: call kvm_vm_check_extension() with the right capability
+ * TODO: call kvm_check_extension() with the right capability
* after the kernel starts implementing it.
*/
cap_ppc_pvr_compat = false;
@@ -151,7 +151,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
exit(1);
}
- cap_rpt_invalidate = kvm_vm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE);
+ cap_rpt_invalidate = kvm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE);
kvm_ppc_register_host_cpu_type();
return 0;
@@ -1968,7 +1968,7 @@ static int kvmppc_get_pvinfo(CPUPPCState *env, struct kvm_ppc_pvinfo *pvinfo)
{
CPUState *cs = env_cpu(env);
- if (kvm_vm_check_extension(cs->kvm_state, KVM_CAP_PPC_GET_PVINFO) &&
+ if (kvm_check_extension(cs->kvm_state, KVM_CAP_PPC_GET_PVINFO) &&
!kvm_vm_ioctl(cs->kvm_state, KVM_PPC_GET_PVINFO, pvinfo)) {
return 0;
}
@@ -2288,7 +2288,7 @@ int kvmppc_reset_htab(int shift_hint)
/* Full emulation, tell caller to allocate htab itself */
return 0;
}
- if (kvm_vm_check_extension(kvm_state, KVM_CAP_PPC_ALLOC_HTAB)) {
+ if (kvm_check_extension(kvm_state, KVM_CAP_PPC_ALLOC_HTAB)) {
int ret;
ret = kvm_vm_ioctl(kvm_state, KVM_PPC_ALLOCATE_HTAB, &shift);
if (ret == -ENOTTY) {
@@ -2484,7 +2484,7 @@ static void kvmppc_get_cpu_characteristics(KVMState *s)
cap_ppc_safe_bounds_check = 0;
cap_ppc_safe_indirect_branch = 0;
- ret = kvm_vm_check_extension(s, KVM_CAP_PPC_GET_CPU_CHAR);
+ ret = kvm_check_extension(s, KVM_CAP_PPC_GET_CPU_CHAR);
if (!ret) {
return;
}
--
2.40.0
