[PATCH v9 13/18] arm64: kexec: add expandable argument to relocation function

From: Pavel Tatashin
Date: Wed Mar 25 2020 - 23:25:00 EST

Currently, kexec relocation function (arm64_relocate_new_kernel) accepts
the following arguments:

head: start of array that contains relocation information.
entry: entry point for new kernel or purgatory.
dtb_mem: first and only argument to entry.

The number of arguments cannot be easily expended, because this
function is also called from HVC_SOFT_RESTART, which preserves only
three arguments. And, also arm64_relocate_new_kernel is written in
assembly but called without stack, thus no place to move extra
arguments to free registers.

Soon, we will need to pass more arguments: once we enable MMU we
will need to pass information about page tables.

Another benefit of allowing this function to accept more arguments, is that
kernel can actually accept up to 4 arguments (x0-x3), however currently
only one is used, but if in the future we will need for more (for example,
pass information about when previous kernel exited to have a precise
measurement in time spent in purgatory), we won't be easilty do that
if arm64_relocate_new_kernel can't accept more arguments.

So, add a new struct: kern_reloc_arg, and place it in kexec safe page (i.e
memory that is not overwritten during relocation).
Thus, make arm64_relocate_new_kernel to only take one argument, that
contains all the needed information.

Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
---
arch/arm64/include/asm/kexec.h | 18 ++++++++++++++++++
arch/arm64/kernel/asm-offsets.c | 9 +++++++++
arch/arm64/kernel/cpu-reset.S | 11 +++--------
arch/arm64/kernel/cpu-reset.h | 8 +++-----
arch/arm64/kernel/machine_kexec.c | 26 ++++++++++++++++++++++++--
arch/arm64/kernel/relocate_kernel.S | 19 ++++++++-----------
6 files changed, 65 insertions(+), 26 deletions(-)

diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
index 9befcd87e9a8..990185744148 100644
--- a/arch/arm64/include/asm/kexec.h
+++ b/arch/arm64/include/asm/kexec.h
@@ -90,12 +90,30 @@ static inline void crash_prepare_suspend(void) {}
static inline void crash_post_resume(void) {}
#endif

+/*
+ * kern_reloc_arg is passed to kernel relocation function as an argument.
+ * head kimage->head, allows to traverse through relocation segments.
+ * entry_addr kimage->start, where to jump from relocation function (new
+ * kernel, or purgatory entry address).
+ * kern_arg0 first argument to kernel is its dtb address. The other
+ * arguments are currently unused, and must be set to 0
+ */
+struct kern_reloc_arg {
+ phys_addr_t head;
+ phys_addr_t entry_addr;
+ phys_addr_t kern_arg0;
+ phys_addr_t kern_arg1;
+ phys_addr_t kern_arg2;
+ phys_addr_t kern_arg3;
+};
+
#define ARCH_HAS_KIMAGE_ARCH

struct kimage_arch {
void *dtb;
phys_addr_t dtb_mem;
phys_addr_t kern_reloc;
+ phys_addr_t kern_reloc_arg;
/* Core ELF header buffer */
void *elf_headers;
unsigned long elf_headers_mem;
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index a5bdce8af65b..448230684749 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -23,6 +23,7 @@
#include <asm/suspend.h>
#include <linux/kbuild.h>
#include <linux/arm-smccc.h>
+#include <linux/kexec.h>

int main(void)
{
@@ -127,6 +128,14 @@ int main(void)
#ifdef CONFIG_ARM_SDE_INTERFACE
DEFINE(SDEI_EVENT_INTREGS, offsetof(struct sdei_registered_event, interrupted_regs));
DEFINE(SDEI_EVENT_PRIORITY, offsetof(struct sdei_registered_event, priority));
+#endif
+#ifdef CONFIG_KEXEC_CORE
+ DEFINE(KEXEC_KRELOC_HEAD, offsetof(struct kern_reloc_arg, head));
+ DEFINE(KEXEC_KRELOC_ENTRY_ADDR, offsetof(struct kern_reloc_arg, entry_addr));
+ DEFINE(KEXEC_KRELOC_KERN_ARG0, offsetof(struct kern_reloc_arg, kern_arg0));
+ DEFINE(KEXEC_KRELOC_KERN_ARG1, offsetof(struct kern_reloc_arg, kern_arg1));
+ DEFINE(KEXEC_KRELOC_KERN_ARG2, offsetof(struct kern_reloc_arg, kern_arg2));
+ DEFINE(KEXEC_KRELOC_KERN_ARG3, offsetof(struct kern_reloc_arg, kern_arg3));
#endif
return 0;
}
diff --git a/arch/arm64/kernel/cpu-reset.S b/arch/arm64/kernel/cpu-reset.S
index 32c7bf858dd9..b8e4b276393e 100644
--- a/arch/arm64/kernel/cpu-reset.S
+++ b/arch/arm64/kernel/cpu-reset.S
@@ -16,14 +16,11 @@
.pushsection .idmap.text, "awx"

/*
- * __cpu_soft_restart(el2_switch, entry, arg0, arg1, arg2) - Helper for
- * cpu_soft_restart.
+ * __cpu_soft_restart(el2_switch, entry, arg) - Helper for cpu_soft_restart.
*
* @el2_switch: Flag to indicate a switch to EL2 is needed.
* @entry: Location to jump to for soft reset.
- * arg0: First argument passed to @entry. (relocation list)
- * arg1: Second argument passed to @entry.(physical kernel entry)
- * arg2: Third argument passed to @entry. (physical dtb address)
+ * arg: Entry argument
*
* Put the CPU into the same state as it would be if it had been reset, and
* branch to what would be the reset vector. It must be executed with the
@@ -43,9 +40,7 @@ ENTRY(__cpu_soft_restart)
hvc #0 // no return

1: mov x8, x1 // entry
- mov x0, x2 // arg0
- mov x1, x3 // arg1
- mov x2, x4 // arg2
+ mov x0, x2 // arg
br x8
ENDPROC(__cpu_soft_restart)

diff --git a/arch/arm64/kernel/cpu-reset.h b/arch/arm64/kernel/cpu-reset.h
index 38cbd4068019..7649eec64f82 100644
--- a/arch/arm64/kernel/cpu-reset.h
+++ b/arch/arm64/kernel/cpu-reset.h
@@ -11,12 +11,10 @@
#include <asm/virt.h>

void __cpu_soft_restart(phys_addr_t el2_switch, phys_addr_t entry,
- phys_addr_t arg0, phys_addr_t arg1, phys_addr_t arg2);
+ phys_addr_t arg);

static inline void __noreturn cpu_soft_restart(phys_addr_t entry,
- phys_addr_t arg0,
- phys_addr_t arg1,
- phys_addr_t arg2)
+ phys_addr_t arg)
{
typeof(__cpu_soft_restart) *restart;

@@ -25,7 +23,7 @@ static inline void __noreturn cpu_soft_restart(phys_addr_t entry,
restart = (void *)__pa_symbol(__cpu_soft_restart);

cpu_install_idmap();
- restart(el2_switch, entry, arg0, arg1, arg2);
+ restart(el2_switch, entry, arg);
unreachable();
}

diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
index cee3be586384..b1122eea627e 100644
--- a/arch/arm64/kernel/machine_kexec.c
+++ b/arch/arm64/kernel/machine_kexec.c
@@ -43,6 +43,7 @@ static void _kexec_image_info(const char *func, int line,
pr_debug(" head: %lx\n", kimage->head);
pr_debug(" nr_segments: %lu\n", kimage->nr_segments);
pr_debug(" kern_reloc: %pa\n", &kimage->arch.kern_reloc);
+ pr_debug(" kern_reloc_arg: %pa\n", &kimage->arch.kern_reloc_arg);

for (i = 0; i < kimage->nr_segments; i++) {
pr_debug(" segment[%lu]: %016lx - %016lx, 0x%lx bytes, %lu pages\n",
@@ -59,13 +60,35 @@ void machine_kexec_cleanup(struct kimage *kimage)
/* Empty routine needed to avoid build errors. */
}

+/* Allocates pages for kexec page table */
+static void *kexec_page_alloc(void *arg)
+{
+ struct kimage *kimage = (struct kimage *)arg;
+ struct page *page = kimage_alloc_control_pages(kimage, 0);
+
+ if (!page)
+ return NULL;
+
+ memset(page_address(page), 0, PAGE_SIZE);
+
+ return page_address(page);
+}
+
int machine_kexec_post_load(struct kimage *kimage)
{
void *reloc_code = page_to_virt(kimage->control_code_page);
+ struct kern_reloc_arg *kern_reloc_arg = kexec_page_alloc(kimage);
+
+ if (!kern_reloc_arg)
+ return -ENOMEM;

memcpy(reloc_code, arm64_relocate_new_kernel,
arm64_relocate_new_kernel_size);
kimage->arch.kern_reloc = __pa(reloc_code);
+ kimage->arch.kern_reloc_arg = __pa(kern_reloc_arg);
+ kern_reloc_arg->head = kimage->head;
+ kern_reloc_arg->entry_addr = kimage->start;
+ kern_reloc_arg->kern_arg0 = kimage->arch.dtb_mem;
kexec_image_info(kimage);

return 0;
@@ -200,8 +223,7 @@ void machine_kexec(struct kimage *kimage)
* userspace (kexec-tools).
* In kexec_file case, the kernel starts directly without purgatory.
*/
- cpu_soft_restart(kimage->arch.kern_reloc, kimage->head, kimage->start,
- kimage->arch.dtb_mem);
+ cpu_soft_restart(kimage->arch.kern_reloc, kimage->arch.kern_reloc_arg);

BUG(); /* Should never get here. */
}
diff --git a/arch/arm64/kernel/relocate_kernel.S b/arch/arm64/kernel/relocate_kernel.S
index 41f9c95fabe8..22ccdcb106d3 100644
--- a/arch/arm64/kernel/relocate_kernel.S
+++ b/arch/arm64/kernel/relocate_kernel.S
@@ -8,6 +8,7 @@

#include <linux/kexec.h>
#include <linux/linkage.h>
+#include <asm/asm-offsets.h>
#include <asm/assembler.h>
#include <asm/kexec.h>
#include <asm/page.h>
@@ -25,12 +26,6 @@
* safe memory that has been set up to be preserved during the copy operation.
*/
ENTRY(arm64_relocate_new_kernel)
- /* Setup the list loop variables. */
- mov x18, x2 /* x18 = dtb address */
- mov x17, x1 /* x17 = kimage_start */
- mov x16, x0 /* x16 = kimage_head */
- mov x14, xzr /* x14 = entry ptr */
- mov x13, xzr /* x13 = copy dest */
/* Clear the sctlr_el2 flags. */
mrs x2, CurrentEL
cmp x2, #CurrentEL_EL2
@@ -42,6 +37,7 @@ ENTRY(arm64_relocate_new_kernel)
msr sctlr_el2, x2
isb
1: /* Check if the new image needs relocation. */
+ ldr x16, [x0, #KEXEC_KRELOC_HEAD] /* x16 = kimage_head */
tbnz x16, IND_DONE_BIT, .Ldone
raw_dcache_line_size x15, x1 /* x15 = dcache line size */
.Lloop:
@@ -81,11 +77,12 @@ ENTRY(arm64_relocate_new_kernel)
isb

/* Start new image. */
- mov x0, x18
- mov x1, xzr
- mov x2, xzr
- mov x3, xzr
- br x17
+ ldr x4, [x0, #KEXEC_KRELOC_ENTRY_ADDR] /* x4 = kimage_start */
+ ldr x3, [x0, #KEXEC_KRELOC_KERN_ARG3]
+ ldr x2, [x0, #KEXEC_KRELOC_KERN_ARG2]
+ ldr x1, [x0, #KEXEC_KRELOC_KERN_ARG1]
+ ldr x0, [x0, #KEXEC_KRELOC_KERN_ARG0] /* x0 = dtb address */
+ br x4
.ltorg
END(arm64_relocate_new_kernel)

--
2.17.1