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

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Date:   Tue, 21 Nov 2023 03:46:41 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>, "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
CC:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        "Nakajima, Jun" <jun.nakajima@...el.com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Hunter, Adrian" <adrian.hunter@...el.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "ashish.kalra@....com" <ashish.kalra@....com>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "bhe@...hat.com" <bhe@...hat.com>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>
Subject: Re: [PATCHv3 10/14] x86/tdx: Convert shared memory back to private on
 kexec


>  
> +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?