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Commit 5dfe9d7d authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Catalin Marinas
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arm64: reduce ID map to a single page 



Commit ea8c2e11 ("arm64: Extend the idmap to the whole kernel
image") changed the early page table code so that the entire kernel
Image is covered by the identity map. This allows functions that
need to enable or disable the MMU to reside anywhere in the kernel
Image.

However, this change has the unfortunate side effect that the Image
cannot cross a physical 512 MB alignment boundary anymore, since the
early page table code cannot deal with the Image crossing a /virtual/
512 MB alignment boundary.

So instead, reduce the ID map to a single page, that is populated by
the contents of the .idmap.text section. Only three functions reside
there at the moment: __enable_mmu(), cpu_resume_mmu() and cpu_reset().
If new code is introduced that needs to manipulate the MMU state, it
should be added to this section as well.

Reviewed-by: default avatarMark Rutland <mark.rutland@arm.com>
Tested-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 61bd93ce

arch/arm64/kernel/head.S

+7 −6
Original line number Diff line number Diff line
@@ -361,7 +361,7 @@ __create_page_tables: 
	 * Create the identity mapping.

	 */

	mov	x0, x25				// idmap_pg_dir

	adrp	x3, KERNEL_START		// __pa(KERNEL_START)

	adrp	x3, __idmap_text_start		// __pa(__idmap_text_start)



#ifndef CONFIG_ARM64_VA_BITS_48

#define EXTRA_SHIFT	(PGDIR_SHIFT + PAGE_SHIFT - 3)
@@ -384,11 +384,11 @@ __create_page_tables: 


	/*

	 * Calculate the maximum allowed value for TCR_EL1.T0SZ so that the

	 * entire kernel image can be ID mapped. As T0SZ == (64 - #bits used),

	 * entire ID map region can be mapped. As T0SZ == (64 - #bits used),

	 * this number conveniently equals the number of leading zeroes in

	 * the physical address of KERNEL_END.

	 * the physical address of __idmap_text_end.

	 */

	adrp	x5, KERNEL_END

	adrp	x5, __idmap_text_end

	clz	x5, x5

	cmp	x5, TCR_T0SZ(VA_BITS)	// default T0SZ small enough?

	b.ge	1f			// .. then skip additional level
@@ -403,8 +403,8 @@ __create_page_tables: 
#endif



	create_pgd_entry x0, x3, x5, x6

	mov	x5, x3				// __pa(KERNEL_START)

	adr_l	x6, KERNEL_END			// __pa(KERNEL_END)

	mov	x5, x3				// __pa(__idmap_text_start)

	adr_l	x6, __idmap_text_end		// __pa(__idmap_text_end)

	create_block_map x0, x7, x3, x5, x6



	/*
@@ -632,6 +632,7 @@ ENDPROC(__secondary_switched) 
 *

 * other registers depend on the function called upon completion

 */

	.section	".idmap.text", "ax"

__enable_mmu:

	ldr	x5, =vectors

	msr	vbar_el1, x5

arch/arm64/kernel/sleep.S

+2 −0
Original line number Diff line number Diff line
@@ -130,12 +130,14 @@ ENDPROC(__cpu_suspend_enter) 
/*

 * x0 must contain the sctlr value retrieved from restored context

 */

	.pushsection	".idmap.text", "ax"

ENTRY(cpu_resume_mmu)

	ldr	x3, =cpu_resume_after_mmu

	msr	sctlr_el1, x0		// restore sctlr_el1

	isb

	br	x3			// global jump to virtual address

ENDPROC(cpu_resume_mmu)

	.popsection

cpu_resume_after_mmu:

	mov	x0, #0			// return zero on success

	ldp	x19, x20, [sp, #16]

arch/arm64/kernel/vmlinux.lds.S

+10 −1
Original line number Diff line number Diff line
@@ -38,6 +38,12 @@ jiffies = jiffies_64; 
	*(.hyp.text)					\

	VMLINUX_SYMBOL(__hyp_text_end) = .;



#define IDMAP_TEXT					\

	. = ALIGN(SZ_4K);				\

	VMLINUX_SYMBOL(__idmap_text_start) = .;		\

	*(.idmap.text)					\

	VMLINUX_SYMBOL(__idmap_text_end) = .;



/*

 * The size of the PE/COFF section that covers the kernel image, which

 * runs from stext to _edata, must be a round multiple of the PE/COFF
@@ -95,6 +101,7 @@ SECTIONS 
			SCHED_TEXT

			LOCK_TEXT

			HYPERVISOR_TEXT

			IDMAP_TEXT

			*(.fixup)

			*(.gnu.warning)

		. = ALIGN(16);
@@ -167,11 +174,13 @@ SECTIONS 
}



/*

 * The HYP init code can't be more than a page long,

 * The HYP init code and ID map text can't be longer than a page each,

 * and should not cross a page boundary.

 */

ASSERT(__hyp_idmap_text_end - (__hyp_idmap_text_start & ~(SZ_4K - 1)) <= SZ_4K,

	"HYP init code too big or misaligned")

ASSERT(__idmap_text_end - (__idmap_text_start & ~(SZ_4K - 1)) <= SZ_4K,

	"ID map text too big or misaligned")



/*

 * If padding is applied before .head.text, virt<->phys conversions will fail.