6.1-stable review patch. If anyone has any objections, please let me know.
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From: Sean Christopherson seanjc@google.com
[ Upstream commit 5e408396c60cd0f0b53a43713016b6d6af8d69e0 ]
Provide dedicated helpers to (un)register virt hooks used during an emergency crash/reboot, and WARN if there is an attempt to overwrite the registered callback, or an attempt to do an unpaired unregister.
Opportunsitically use rcu_assign_pointer() instead of RCU_INIT_POINTER(), mainly so that the set/unset paths are more symmetrical, but also because any performance gains from using RCU_INIT_POINTER() are meaningless for this code.
Reviewed-by: Kai Huang kai.huang@intel.com Link: https://lore.kernel.org/r/20230721201859.2307736-3-seanjc@google.com Signed-off-by: Sean Christopherson seanjc@google.com Stable-dep-of: a0ee1d5faff1 ("KVM: VMX: Flush shadow VMCS on emergency reboot") Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/reboot.h | 5 +++-- arch/x86/kernel/reboot.c | 30 ++++++++++++++++++++++++------ arch/x86/kvm/vmx/vmx.c | 6 ++---- 3 files changed, 29 insertions(+), 12 deletions(-)
--- a/arch/x86/include/asm/reboot.h +++ b/arch/x86/include/asm/reboot.h @@ -25,8 +25,9 @@ void __noreturn machine_real_restart(uns #define MRR_BIOS 0 #define MRR_APM 1
-typedef void crash_vmclear_fn(void); -extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss; +typedef void (cpu_emergency_virt_cb)(void); +void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback); +void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callback); void cpu_emergency_disable_virtualization(void);
typedef void (*nmi_shootdown_cb)(int, struct pt_regs*); --- a/arch/x86/kernel/reboot.c +++ b/arch/x86/kernel/reboot.c @@ -794,17 +794,35 @@ void machine_crash_shutdown(struct pt_re * * protected by rcu. */ -crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss; -EXPORT_SYMBOL_GPL(crash_vmclear_loaded_vmcss); +static cpu_emergency_virt_cb __rcu *cpu_emergency_virt_callback; + +void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback) +{ + if (WARN_ON_ONCE(rcu_access_pointer(cpu_emergency_virt_callback))) + return; + + rcu_assign_pointer(cpu_emergency_virt_callback, callback); +} +EXPORT_SYMBOL_GPL(cpu_emergency_register_virt_callback); + +void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callback) +{ + if (WARN_ON_ONCE(rcu_access_pointer(cpu_emergency_virt_callback) != callback)) + return; + + rcu_assign_pointer(cpu_emergency_virt_callback, NULL); + synchronize_rcu(); +} +EXPORT_SYMBOL_GPL(cpu_emergency_unregister_virt_callback);
static inline void cpu_crash_vmclear_loaded_vmcss(void) { - crash_vmclear_fn *do_vmclear_operation = NULL; + cpu_emergency_virt_cb *callback;
rcu_read_lock(); - do_vmclear_operation = rcu_dereference(crash_vmclear_loaded_vmcss); - if (do_vmclear_operation) - do_vmclear_operation(); + callback = rcu_dereference(cpu_emergency_virt_callback); + if (callback) + callback(); rcu_read_unlock(); }
--- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -8602,8 +8602,7 @@ static void __vmx_exit(void) { allow_smaller_maxphyaddr = false;
- RCU_INIT_POINTER(crash_vmclear_loaded_vmcss, NULL); - synchronize_rcu(); + cpu_emergency_unregister_virt_callback(crash_vmclear_local_loaded_vmcss);
vmx_cleanup_l1d_flush(); } @@ -8677,8 +8676,7 @@ static int __init vmx_init(void) pi_init_cpu(cpu); }
- rcu_assign_pointer(crash_vmclear_loaded_vmcss, - crash_vmclear_local_loaded_vmcss); + cpu_emergency_register_virt_callback(crash_vmclear_local_loaded_vmcss);
vmx_check_vmcs12_offsets();