linux-kernel - [RFC PATCH v2 03/16] x86/kexec: Restore GDT on return from preserve

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Message-ID: <20241122224715.171751-4-dwmw2@infradead.org>
Date: Fri, 22 Nov 2024 22:38:12 +0000
From: David Woodhouse <dwmw2@...radead.org>
To: kexec@...ts.infradead.org
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,
	"H. Peter Anvin" <hpa@...or.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Kai Huang <kai.huang@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	linux-kernel@...r.kernel.org,
	Simon Horman <horms@...nel.org>,
	Dave Young <dyoung@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	jpoimboe@...nel.org
Subject: [RFC PATCH v2 03/16] x86/kexec: Restore GDT on return from preserve_context kexec

From: David Woodhouse <dwmw@...zon.co.uk>

The restore_processor_state() function explicitly states that "the asm code
that gets us here will have restored a usable GDT". That wasn't true in the
case of returning from a preserve_context kexec. Make it so.

Without this, the kernel was depending on the called function to reload an
appropriate GDT.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
 arch/x86/kernel/relocate_kernel_64.S | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index ca01e3e2f097..ed2ae50535dd 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -252,6 +252,11 @@ SYM_CODE_START_LOCAL_NOALIGN(virtual_mapped)
 	movq	CR0(%r8), %r8
 	movq	%rax, %cr3
 	movq	%r8, %cr0
+
+	/* Saved in save_processor_state. */
+	movq    $saved_context, %rax
+	lgdt    saved_context_gdt_desc(%rax)
+
 	movq	%rbp, %rax
 
 	popf
-- 
2.47.0