Commit 380e18ad authored by Quentin Perret's avatar Quentin Perret Committed by Marc Zyngier
Browse files

KVM: arm64: Introduce a BSS section for use at Hyp 



Currently, the hyp code cannot make full use of a bss, as the kernel
section is mapped read-only.

While this mapping could simply be changed to read-write, it would
intermingle even more the hyp and kernel state than they currently are.
Instead, introduce a __hyp_bss section, that uses reserved pages, and
create the appropriate RW hyp mappings during KVM init.

Acked-by: default avatarWill Deacon <will@kernel.org>
Signed-off-by: default avatarQuentin Perret <qperret@google.com>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210319100146.1149909-8-qperret@google.com
parent 7aef0cbc

arch/arm64/include/asm/sections.h

+1 −0
Original line number Diff line number Diff line
@@ -13,6 +13,7 @@ extern char __hyp_idmap_text_start[], __hyp_idmap_text_end[]; 
extern char __hyp_text_start[], __hyp_text_end[];

extern char __hyp_rodata_start[], __hyp_rodata_end[];

extern char __hyp_reloc_begin[], __hyp_reloc_end[];

extern char __hyp_bss_start[], __hyp_bss_end[];

extern char __idmap_text_start[], __idmap_text_end[];

extern char __initdata_begin[], __initdata_end[];

extern char __inittext_begin[], __inittext_end[];

arch/arm64/kernel/vmlinux.lds.S

+34 −18
Original line number Diff line number Diff line
@@ -5,24 +5,7 @@ 
 * Written by Martin Mares <mj@atrey.karlin.mff.cuni.cz>

 */



#define RO_EXCEPTION_TABLE_ALIGN	8

#define RUNTIME_DISCARD_EXIT



#include <asm-generic/vmlinux.lds.h>

#include <asm/cache.h>

#include <asm/hyp_image.h>

#include <asm/kernel-pgtable.h>

#include <asm/memory.h>

#include <asm/page.h>



#include "image.h"



OUTPUT_ARCH(aarch64)

ENTRY(_text)



jiffies = jiffies_64;





#ifdef CONFIG_KVM

#define HYPERVISOR_EXTABLE					\

	. = ALIGN(SZ_8);					\
@@ -51,13 +34,43 @@ jiffies = jiffies_64; 
		__hyp_reloc_end = .;				\

	}



#define BSS_FIRST_SECTIONS					\

	__hyp_bss_start = .;					\

	*(HYP_SECTION_NAME(.bss))				\

	. = ALIGN(PAGE_SIZE);					\

	__hyp_bss_end = .;



/*

 * We require that __hyp_bss_start and __bss_start are aligned, and enforce it

 * with an assertion. But the BSS_SECTION macro places an empty .sbss section

 * between them, which can in some cases cause the linker to misalign them. To

 * work around the issue, force a page alignment for __bss_start.

 */

#define SBSS_ALIGN			PAGE_SIZE

#else /* CONFIG_KVM */

#define HYPERVISOR_EXTABLE

#define HYPERVISOR_DATA_SECTIONS

#define HYPERVISOR_PERCPU_SECTION

#define HYPERVISOR_RELOC_SECTION

#define SBSS_ALIGN			0

#endif



#define RO_EXCEPTION_TABLE_ALIGN	8

#define RUNTIME_DISCARD_EXIT



#include <asm-generic/vmlinux.lds.h>

#include <asm/cache.h>

#include <asm/kernel-pgtable.h>

#include <asm/memory.h>

#include <asm/page.h>



#include "image.h"



OUTPUT_ARCH(aarch64)

ENTRY(_text)



jiffies = jiffies_64;



#define HYPERVISOR_TEXT					\

	/*						\

	 * Align to 4 KB so that			\
@@ -276,7 +289,7 @@ SECTIONS 
	__pecoff_data_rawsize = ABSOLUTE(. - __initdata_begin);

	_edata = .;



	BSS_SECTION(0, 0, 0)

	BSS_SECTION(SBSS_ALIGN, 0, 0)



	. = ALIGN(PAGE_SIZE);

	init_pg_dir = .;
@@ -324,6 +337,9 @@ ASSERT(__hibernate_exit_text_end - (__hibernate_exit_text_start & ~(SZ_4K - 1)) 
ASSERT((__entry_tramp_text_end - __entry_tramp_text_start) == PAGE_SIZE,

	"Entry trampoline text too big")

#endif

#ifdef CONFIG_KVM

ASSERT(__hyp_bss_start == __bss_start, "HYP and Host BSS are misaligned")

#endif

/*

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

 */

arch/arm64/kvm/arm.c

+13 −1
Original line number Diff line number Diff line
@@ -1775,7 +1775,19 @@ static int init_hyp_mode(void) 
		goto out_err;

	}



	err = create_hyp_mappings(kvm_ksym_ref(__bss_start),

	/*

	 * .hyp.bss is guaranteed to be placed at the beginning of the .bss

	 * section thanks to an assertion in the linker script. Map it RW and

	 * the rest of .bss RO.

	 */

	err = create_hyp_mappings(kvm_ksym_ref(__hyp_bss_start),

				  kvm_ksym_ref(__hyp_bss_end), PAGE_HYP);

	if (err) {

		kvm_err("Cannot map hyp bss section: %d\n", err);

		goto out_err;

	}



	err = create_hyp_mappings(kvm_ksym_ref(__hyp_bss_end),

				  kvm_ksym_ref(__bss_stop), PAGE_HYP_RO);

	if (err) {

		kvm_err("Cannot map bss section\n");

arch/arm64/kvm/hyp/nvhe/hyp.lds.S

+1 −0
Original line number Diff line number Diff line
@@ -25,4 +25,5 @@ SECTIONS { 
	BEGIN_HYP_SECTION(.data..percpu)

		PERCPU_INPUT(L1_CACHE_BYTES)

	END_HYP_SECTION

	HYP_SECTION(.bss)

}