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 12:36:09 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: "Kalra, Ashish" <ashish.kalra@....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

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());
 }
 
-- 
  Kiryl Shutsemau / Kirill A. Shutemov