| Message ID | 20250114175143.81438-19-vschneid@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | context_tracking,x86: Defer some IPIs until a user->kernel transition | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
Please use "KVM: VMX:" for the scope. On Tue, Jan 14, 2025, Valentin Schneider wrote: > Later commits will cause objtool to warn about static keys being used in > .noinstr sections in order to safely defer instruction patching IPIs > targeted at NOHZ_FULL CPUs. > > These keys are used in .noinstr code, and can be modified at runtime > (/proc/kernel/vmx* write). However it is not expected that they will be > flipped during latency-sensitive operations, and thus shouldn't be a source > of interference wrt the text patching IPI. This misses KVM's static key that's buried behind CONFIG_HYPERV=m|y. vmlinux.o: warning: objtool: vmx_vcpu_enter_exit+0x241: __kvm_is_using_evmcs: non-RO static key usage in noinstr vmlinux.o: warning: objtool: vmx_update_host_rsp+0x13: __kvm_is_using_evmcs: non-RO static key usage in noinstr Side topic, it's super annoying that "objtool --noinstr" only runs on vmlinux.o. I realize objtool doesn't have the visilibity to validate cross-object calls, but couldn't objtool validates calls and static key/branch usage so long as the target or key/branch is defined in the same object?
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 893366e537322..a028c38f44e02 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -225,8 +225,15 @@ module_param(pt_mode, int, S_IRUGO); struct x86_pmu_lbr __ro_after_init vmx_lbr_caps; -static DEFINE_STATIC_KEY_FALSE(vmx_l1d_should_flush); -static DEFINE_STATIC_KEY_FALSE(vmx_l1d_flush_cond); +/* + * Both of these static keys end up being used in .noinstr sections, however + * they are only modified: + * - at init + * - from a /proc/kernel/vmx* write + * thus during latency-sensitive operations they should remain stable. + */ +static DEFINE_STATIC_KEY_FALSE_NOINSTR(vmx_l1d_should_flush); +static DEFINE_STATIC_KEY_FALSE_NOINSTR(vmx_l1d_flush_cond); static DEFINE_MUTEX(vmx_l1d_flush_mutex); /* Storage for pre module init parameter parsing */
Later commits will cause objtool to warn about static keys being used in .noinstr sections in order to safely defer instruction patching IPIs targeted at NOHZ_FULL CPUs. These keys are used in .noinstr code, and can be modified at runtime (/proc/kernel/vmx* write). However it is not expected that they will be flipped during latency-sensitive operations, and thus shouldn't be a source of interference wrt the text patching IPI. Mark it to let objtool know not to warn about it. Reported-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Valentin Schneider <vschneid@redhat.com> --- arch/x86/kvm/vmx/vmx.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)