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

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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: Will Deacon <will@kernel.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210319100146.1149909-8-qperret@google.com
This commit is contained in:
Quentin Perret 2021-03-19 10:01:15 +00:00 committed by Marc Zyngier
parent 7aef0cbcdc
commit 380e18ade4
4 changed files with 49 additions and 19 deletions
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1
arch/arm64/include/asm/sections.h
View file

@ -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[];

52
arch/arm64/kernel/vmlinux.lds.S
View file

@ -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.
*/

14
arch/arm64/kvm/arm.c
View file

@ -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");

1
arch/arm64/kvm/hyp/nvhe/hyp.lds.S
View file

@ -25,4 +25,5 @@ SECTIONS {
BEGIN_HYP_SECTION(.data..percpu)
PERCPU_INPUT(L1_CACHE_BYTES)
END_HYP_SECTION
HYP_SECTION(.bss)
}