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x86/reboot: Harden virtualization hooks for emergency reboot

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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>
This commit is contained in:
Sean Christopherson 2023-07-21 13:18:42 -07:00
parent b23c83ad2c
commit 5e408396c6
3 changed files with 29 additions and 12 deletions
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5
arch/x86/include/asm/reboot.h
View File

@ -25,8 +25,9 @@ void __noreturn machine_real_restart(unsigned int type);
#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*);

30
arch/x86/kernel/reboot.c
View File

@ -794,17 +794,35 @@ void machine_crash_shutdown(struct pt_regs *regs)
*
* 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();
}

6
arch/x86/kvm/vmx/vmx.c
View File

@ -8571,8 +8571,7 @@ 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();
}
@ -8620,8 +8619,7 @@ 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();