Re: [PATCHv3 10/14] x86/tdx: Convert shared memory back to private on kexec

[Huang, Kai]

>  
> +static atomic_t conversions_in_progress;
> +static bool conversion_allowed = true;
> 

[...]

>  /* Used while preparing memory map entries for second kernel */
>  struct crash_memmap_data {
> @@ -107,6 +108,9 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
>  
>  	crash_smp_send_stop();
>  
> +	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
> +		x86_platform.guest.enc_kexec_unshare_mem(true);
> +
>  	cpu_emergency_disable_virtualization();
>  
>  	/*
> diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> index 830425e6d38e..9fb302562bfd 100644
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -12,6 +12,7 @@
>  #include <linux/delay.h>
>  #include <linux/objtool.h>
>  #include <linux/pgtable.h>
> +#include <linux/kexec.h>
>  #include <acpi/reboot.h>
>  #include <asm/io.h>
>  #include <asm/apic.h>
> @@ -31,6 +32,7 @@
>  #include <asm/realmode.h>
>  #include <asm/x86_init.h>
>  #include <asm/efi.h>
> +#include <asm/tdx.h>
>  
>  /*
>   * Power off function, if any
> @@ -716,6 +718,9 @@ static void native_machine_emergency_restart(void)
>  
>  void native_machine_shutdown(void)
>  {
> +	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) && kexec_in_progress)
> +		x86_platform.guest.enc_kexec_unshare_mem(false);
> +
>  	/* Stop the cpus and apics */
>  #ifdef CONFIG_X86_IO_APIC
>  	/*

In native_machine_crash_shutdown() the "unshare" is called after
crash_smp_send_stop(), but here it's called before the stop_other_cpus().

I am wondering if you call "unshare" after stop_other_cpus(), can we guarantee
there's only one cpu running in both normal and crash kexec in which case you
might be able to get rid of the "conversions_in_progress" and
"conversion_allowed" above?