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 <w...@kernel.org> Signed-off-by: Quentin Perret <qper...@google.com> --- arch/arm64/include/asm/sections.h | 1 + arch/arm64/kernel/vmlinux.lds.S | 52 ++++++++++++++++++++----------- arch/arm64/kvm/arm.c | 14 ++++++++- arch/arm64/kvm/hyp/nvhe/hyp.lds.S | 1 + 4 files changed, 49 insertions(+), 19 deletions(-) diff --git a/arch/arm64/include/asm/sections.h b/arch/arm64/include/asm/sections.h index 2f36b16a5b5d..e4ad9db53af1 100644 --- a/arch/arm64/include/asm/sections.h +++ b/arch/arm64/include/asm/sections.h @@ -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[]; diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 7eea7888bb02..e96173ce211b 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -5,24 +5,7 @@ * Written by Martin Mares <m...@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. */ diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 2d1e7ef69c04..3f8bcf8db036 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -1770,7 +1770,19 @@ 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"); diff --git a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S index cd119d82d8e3..f4562f417d3f 100644 --- a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S +++ b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S @@ -25,4 +25,5 @@ SECTIONS { BEGIN_HYP_SECTION(.data..percpu) PERCPU_INPUT(L1_CACHE_BYTES) END_HYP_SECTION + HYP_SECTION(.bss) } -- 2.30.1.766.gb4fecdf3b7-goog _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm