linux-kernel - Re: [PATCHv6 10/16] x86/tdx: Convert shared memory back to private on kexec

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Date: Mon, 29 Jan 2024 07:09:37 -0600
From: "Kalra, Ashish" <ashish.kalra@....com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "Rafael J. Wysocki" <rafael@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
 Elena Reshetova <elena.reshetova@...el.com>,
 Jun Nakajima <jun.nakajima@...el.com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>,
 Tom Lendacky <thomas.lendacky@....com>,
 Sean Christopherson <seanjc@...gle.com>, "Huang, Kai" <kai.huang@...el.com>,
 Baoquan He <bhe@...hat.com>, kexec@...ts.infradead.org,
 linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv6 10/16] x86/tdx: Convert shared memory back to private on
 kexec

Hello Kirill,

On 1/29/2024 4:36 AM, Kirill A. Shutemov wrote:
> On Mon, Jan 29, 2024 at 04:24:09AM -0600, Kalra, Ashish wrote:
>> In case of SNP and crash/kdump case, we need to prevent the boot_ghcb being
>> converted to shared (in snp_kexec_unshare_mem()) as the boot_ghcb is
>> required to handle all I/O for disabling IO-APIC/lapic, hpet, etc., as the
>> enc_kexec_unshare_mem() callback is invoked before the apics, hpet, etc. are
>> disabled.
>>
>> Is there any reason why enc_kexec_unshare_mem() callback is invoked in crash
>> case before the IO-APIC/lapic, hpet, etc. are shutdown/disabled ?
> Not really. Either way works for TDX. I've tested the patch below. Is it
> what you want?
>
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 6585a5f2c2ba..3001f4857ed7 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -107,11 +107,6 @@ 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_stop_conversion(true);
> -		x86_platform.guest.enc_kexec_unshare_mem();
> -	}
> -
>   	cpu_emergency_disable_virtualization();
>   
>   	/*
> @@ -129,6 +124,12 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
>   #ifdef CONFIG_HPET_TIMER
>   	hpet_disable();
>   #endif
> +
> +	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
> +		x86_platform.guest.enc_kexec_stop_conversion(true);
> +		x86_platform.guest.enc_kexec_unshare_mem();
> +	}
> +
>   	crash_save_cpu(regs, safe_smp_processor_id());
>   }
>   

Yes, this will work for SNP.

Thanks, Ashish