linux-kernel - Re: [PATCH] x86/boot/compressed: Exclude 'top

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Date:   Thu, 3 May 2018 13:52:05 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Hugh Dickins <hughd@...gle.com>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] x86/boot/compressed: Exclude 'top_pgtable' from
 relocation

On Thu, May 03, 2018 at 08:38:49AM +0000, Kirill A. Shutemov wrote:
> The patch is bogus and I still don't understand what is going on.

I think I found the issue. Could you check the patch below:

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index fca012baba19..86169ae1c536 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -370,10 +370,13 @@ trampoline_return:
 	/*
 	 * cleanup_trampoline() would restore trampoline memory.
 	 *
+	 * RDI is address of the page table to use (if required).
+	 *
 	 * RSI holds real mode data and needs to be preserved across
 	 * this function call.
 	 */
 	pushq	%rsi
+	leaq	top_pgtable(%rbx), %rdi
 	call	cleanup_trampoline
 	popq	%rsi
 
@@ -647,5 +650,14 @@ boot_stack_end:
  */
 	.section ".pgtable","a",@nobits
 	.balign 4096
+	.global pgtable
 pgtable:
 	.fill BOOT_PGT_SIZE, 1, 0
+
+/*
+ * The page table is going to be used instead of page table in the trampoline
+ * memory.
+ */
+	.global top_pgtable
+top_pgtable:
+	.fill PAGE_SIZE, 1, 0
diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index 32af1cbcd903..a362fa0b849c 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -22,14 +22,6 @@ struct paging_config {
 /* Buffer to preserve trampoline memory */
 static char trampoline_save[TRAMPOLINE_32BIT_SIZE];
 
-/*
- * The page table is going to be used instead of page table in the trampoline
- * memory.
- *
- * It must not be in BSS as BSS is cleared after cleanup_trampoline().
- */
-static char top_pgtable[PAGE_SIZE] __aligned(PAGE_SIZE) __section(.data);
-
 /*
  * Trampoline address will be printed by extract_kernel() for debugging
  * purposes.
@@ -134,7 +126,7 @@ struct paging_config paging_prepare(void)
 	return paging_config;
 }
 
-void cleanup_trampoline(void)
+void cleanup_trampoline(void *pgtable)
 {
 	void *trampoline_pgtable;
 
@@ -145,8 +137,8 @@ void cleanup_trampoline(void)
 	 * if it's there.
 	 */
 	if ((void *)__native_read_cr3() == trampoline_pgtable) {
-		memcpy(top_pgtable, trampoline_pgtable, PAGE_SIZE);
-		native_write_cr3((unsigned long)top_pgtable);
+		memcpy(pgtable, trampoline_pgtable, PAGE_SIZE);
+		native_write_cr3((unsigned long)pgtable);
 	}
 
 	/* Restore trampoline memory */
-- 
 Kirill A. Shutemov