linux-kernel - Re: [PATCH] ARM: kexec: Fix panic after TLB are invalidated

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Message-ID: <20210201130344.GF1463@shell.armlinux.org.uk>
Date:   Mon, 1 Feb 2021 13:03:45 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Giancarlo Ferrari <giancarlo.ferrari89@...il.com>,
        linux-kernel@...r.kernel.org, penberg@...nel.org,
        geert@...ux-m68k.org, linux-arm-kernel@...ts.infradead.org,
        akpm@...ux-foundation.org, rppt@...nel.org,
        giancarlo.ferrari@...ia.com
Subject: Re: [PATCH] ARM: kexec: Fix panic after TLB are invalidated

On Mon, Feb 01, 2021 at 12:47:20PM +0000, Mark Rutland wrote:
> 1. copy reloc code into buffer
> 2. alter variables in copy of reloc code
> 3. branch to buffer
> 
> ... which would avoid this class of problem too.

Yep, slightly messy to do though:

diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
index 5d84ad333f05..6058e0d3a40d 100644
--- a/arch/arm/kernel/machine_kexec.c
+++ b/arch/arm/kernel/machine_kexec.c
@@ -174,18 +174,27 @@ void machine_kexec(struct kimage *image)
 
 	reboot_code_buffer = page_address(image->control_code_page);
 
-	/* Prepare parameters for reboot_code_buffer*/
-	set_kernel_text_rw();
-	kexec_start_address = image->start;
-	kexec_indirection_page = page_list;
-	kexec_mach_type = machine_arch_type;
-	kexec_boot_atags = image->arch.kernel_r2;
-
 	/* copy our kernel relocation code to the control code page */
 	reboot_entry = fncpy(reboot_code_buffer,
 			     &relocate_new_kernel,
 			     relocate_new_kernel_size);
 
+#define set(what, val) \
+	do { \
+		uintptr_t __funcp_address; \
+		int __offset; \
+		void *__ptr; \
+		asm("" : "=r" (__funcp_address) : "0" (&relocate_new_kernel)); \
+		__offset = (uintptr_t)&(what) - (__funcp_address & ~1); \
+		__ptr = reboot_code_buffer + __offset; \
+		*(__typeof__(&(what)))__ptr = val; \
+	} while (0)
+
+	set(kexec_start_address, image->start);
+	set(kexec_indirection_page, page_list);
+	set(kexec_mach_type, machine_arch_type);
+	set(kexec_boot_atags, image->arch.kernel_r2);
+
 	/* get the identity mapping physical address for the reboot code */
 	reboot_entry_phys = virt_to_idmap(reboot_entry);
 
-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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