x86/decompressor: Merge trampoline cleanup with switching code

Now that the trampoline setup code and the actual invocation of it are
all done from the C routine, the trampoline cleanup can be merged into
it as well, instead of returning to asm just to call another C function.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: https://lore.kernel.org/r/20230807162720.545787-16-ardb@kernel.org

Author: ardbiesheuvel

arch/x86/boot/compressed/head_64.S

@@ -430,20 +430,14 @@ SYM_CODE_START(startup_64)
 	 * a trampoline in 32-bit addressable memory if the current number does
 	 * not match the desired number.
 	 *
-	 * Pass the boot_params pointer as the first argument.
+	 * Pass the boot_params pointer as the first argument. The second
+	 * argument is the relocated address of the page table to use instead
+	 * of the page table in trampoline memory (if required).
 	 */
 	movq	%r15, %rdi
+	leaq	rva(top_pgtable)(%rbx), %rsi
 	call	configure_5level_paging
 
-	/*
-	 * cleanup_trampoline() would restore trampoline memory.
-	 *
-	 * RDI is address of the page table to use instead of page table
-	 * in trampoline memory (if required).
-	 */
-	leaq	rva(top_pgtable)(%rbx), %rdi
-	call	cleanup_trampoline
-
 	/* Zero EFLAGS */
 	pushq	$0
 	popfq

arch/x86/boot/compressed/pgtable_64.c

@@ -101,7 +101,7 @@ static unsigned long find_trampoline_placement(void)
 	return bios_start - TRAMPOLINE_32BIT_SIZE;
 }
 
-asmlinkage void configure_5level_paging(struct boot_params *bp)
+asmlinkage void configure_5level_paging(struct boot_params *bp, void *pgtable)
 {
 	void (*toggle_la57)(void *cr3);
 	bool l5_required = false;
@@ -191,22 +191,12 @@ asmlinkage void configure_5level_paging(struct boot_params *bp)
 	}
 
 	toggle_la57(trampoline_32bit);
-}
-
-void cleanup_trampoline(void *pgtable)
-{
-	void *trampoline_pgtable;
-
-	trampoline_pgtable = trampoline_32bit;
 
 	/*
-	 * Move the top level page table out of trampoline memory,
-	 * if it's there.
+	 * Move the top level page table out of trampoline memory.
 	 */
-	if ((void *)__native_read_cr3() == trampoline_pgtable) {
-		memcpy(pgtable, trampoline_pgtable, PAGE_SIZE);
-		native_write_cr3((unsigned long)pgtable);
-	}
+	memcpy(pgtable, trampoline_32bit, PAGE_SIZE);
+	native_write_cr3((unsigned long)pgtable);
 
 	/* Restore trampoline memory */
 	memcpy(trampoline_32bit, trampoline_save, TRAMPOLINE_32BIT_SIZE);