Commit f8b8ee45 authored by H. Peter Anvin (Intel)'s avatar H. Peter Anvin (Intel) Committed by Borislav Petkov (AMD)
Browse files

x86/fred: Add a NMI entry stub for FRED 



On a FRED system, NMIs nest both with themselves and faults, transient
information is saved into the stack frame, and NMI unblocking only
happens when the stack frame indicates that so should happen.

Thus, the NMI entry stub for FRED is really quite small...

Signed-off-by: default avatarH. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: default avatarXin Li <xin3.li@intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Tested-by: default avatarShan Kang <shan.kang@intel.com>
Link: https://lore.kernel.org/r/20231216063139.25567-1-xin3.li@intel.com
parent 99fcc968

arch/x86/kernel/nmi.c

+42 −0
Original line number Diff line number Diff line
@@ -35,6 +35,7 @@ 
#include <asm/nospec-branch.h>

#include <asm/microcode.h>

#include <asm/sev.h>

#include <asm/fred.h>



#define CREATE_TRACE_POINTS

#include <trace/events/nmi.h>
@@ -651,6 +652,47 @@ void nmi_backtrace_stall_check(const struct cpumask *btp) 


#endif



#ifdef CONFIG_X86_FRED

/*

 * With FRED, CR2/DR6 is pushed to #PF/#DB stack frame during FRED

 * event delivery, i.e., there is no problem of transient states.

 * And NMI unblocking only happens when the stack frame indicates

 * that so should happen.

 *

 * Thus, the NMI entry stub for FRED is really straightforward and

 * as simple as most exception handlers. As such, #DB is allowed

 * during NMI handling.

 */

DEFINE_FREDENTRY_NMI(exc_nmi)

{

	irqentry_state_t irq_state;



	if (arch_cpu_is_offline(smp_processor_id())) {

		if (microcode_nmi_handler_enabled())

			microcode_offline_nmi_handler();

		return;

	}



	/*

	 * Save CR2 for eventual restore to cover the case where the NMI

	 * hits the VMENTER/VMEXIT region where guest CR2 is life. This

	 * prevents guest state corruption in case that the NMI handler

	 * takes a page fault.

	 */

	this_cpu_write(nmi_cr2, read_cr2());



	irq_state = irqentry_nmi_enter(regs);



	inc_irq_stat(__nmi_count);

	default_do_nmi(regs);



	irqentry_nmi_exit(regs, irq_state);



	if (unlikely(this_cpu_read(nmi_cr2) != read_cr2()))

		write_cr2(this_cpu_read(nmi_cr2));

}

#endif



void stop_nmi(void)

{

	ignore_nmis++;