[PATCH v4 15/17] arm64: kexec: add expandable argument to relocation function

From: Pavel Tatashin
Date: Mon Sep 09 2019 - 14:13:00 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 | 4 +-
arch/arm64/kernel/cpu-reset.h | 8 +--
arch/arm64/kernel/machine_kexec.c | 29 +++++++++-
arch/arm64/kernel/relocate_kernel.S | 88 ++++++++++-------------------
6 files changed, 87 insertions(+), 69 deletions(-)

diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
index d15ca1ca1e83..d5b79d4c7fae 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 {
+ unsigned long head;
+ unsigned long entry_addr;
+ unsigned long kern_arg0;
+ unsigned long kern_arg1;
+ unsigned long kern_arg2;
+ unsigned long kern_arg3;
+};
+
#define ARCH_HAS_KIMAGE_ARCH

struct kimage_arch {
void *dtb;
unsigned long dtb_mem;
unsigned long kern_reloc;
+ unsigned long kern_reloc_arg;
};

#ifdef CONFIG_KEXEC_FILE
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 214685760e1c..900394907fd8 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)
{
@@ -126,6 +127,14 @@ 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(KRELOC_HEAD, offsetof(struct kern_reloc_arg, head));
+ DEFINE(KRELOC_ENTRY_ADDR, offsetof(struct kern_reloc_arg, entry_addr));
+ DEFINE(KRELOC_KERN_ARG0, offsetof(struct kern_reloc_arg, kern_arg0));
+ DEFINE(KRELOC_KERN_ARG1, offsetof(struct kern_reloc_arg, kern_arg1));
+ DEFINE(KRELOC_KERN_ARG2, offsetof(struct kern_reloc_arg, kern_arg2));
+ DEFINE(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 6ea337d464c4..64c78a42919f 100644
--- a/arch/arm64/kernel/cpu-reset.S
+++ b/arch/arm64/kernel/cpu-reset.S
@@ -43,9 +43,7 @@ ENTRY(__cpu_soft_restart)
hvc #0 // no return

1: mov x18, x1 // entry
- mov x0, x2 // arg0
- mov x1, x3 // arg1
- mov x2, x4 // arg2
+ mov x0, x2 // arg
br x18
ENDPROC(__cpu_soft_restart)

diff --git a/arch/arm64/kernel/cpu-reset.h b/arch/arm64/kernel/cpu-reset.h
index ed50e9587ad8..7a8720ff186f 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(unsigned long el2_switch, unsigned long entry,
- unsigned long arg0, unsigned long arg1, unsigned long arg2);
+ unsigned long arg);

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

@@ -25,7 +23,7 @@ static inline void __noreturn cpu_soft_restart(unsigned long 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 9b41da50e6f7..fb6138a1c9ff 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",
@@ -59,14 +60,39 @@ 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)
{
unsigned long kern_reloc;
+ struct kern_reloc_arg *kern_reloc_arg;

kern_reloc = page_to_phys(kimage->control_code_page);
memcpy(__va(kern_reloc), arm64_relocate_new_kernel,
arm64_relocate_new_kernel_size);
+
+ kern_reloc_arg = kexec_page_alloc(kimage);
+ if (!kern_reloc_arg)
+ return -ENOMEM;
+
kimage->arch.kern_reloc = kern_reloc;
+ 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;
@@ -203,8 +229,7 @@ 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 c1d7db71a726..d352faf7cbe6 100644
--- a/arch/arm64/kernel/relocate_kernel.S
+++ b/arch/arm64/kernel/relocate_kernel.S
@@ -8,7 +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>
@@ -17,86 +17,58 @@
/*
* arm64_relocate_new_kernel - Put a 2nd stage image in place and boot it.
*
- * The memory that the old kernel occupies may be overwritten when coping the
+ * The memory that the old kernel occupies may be overwritten when copying the
* new image to its final location. To assure that the
* arm64_relocate_new_kernel routine which does that copy is not overwritten,
* all code and data needed by arm64_relocate_new_kernel must be between the
* symbols arm64_relocate_new_kernel and arm64_relocate_new_kernel_end. The
* machine_kexec() routine will copy arm64_relocate_new_kernel to the kexec
- * control_code_page, a special page which has been set up to be preserved
- * during the copy operation.
+ * 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 */
- raw_dcache_line_size x15, x0 /* x15 = dcache line size */
- mov x14, xzr /* x14 = entry ptr */
- mov x13, xzr /* x13 = copy dest */
-
/* Clear the sctlr_el2 flags. */
- mrs x0, CurrentEL
- cmp x0, #CurrentEL_EL2
+ mrs x2, CurrentEL
+ cmp x2, #CurrentEL_EL2
b.ne 1f
- mrs x0, sctlr_el2
+ mrs x2, sctlr_el2
ldr x1, =SCTLR_ELx_FLAGS
- bic x0, x0, x1
+ bic x2, x2, x1
pre_disable_mmu_workaround
- msr sctlr_el2, x0
+ msr sctlr_el2, x2
isb
-1:
-
- /* Check if the new image needs relocation. */
+1: /* Check if the new image needs relocation. */
+ ldr x16, [x0, #KRELOC_HEAD] /* x16 = kimage_head */
tbnz x16, IND_DONE_BIT, .Ldone
-
+ raw_dcache_line_size x15, x1 /* x15 = dcache line size */
.Lloop:
and x12, x16, PAGE_MASK /* x12 = addr */
-
/* Test the entry flags. */
.Ltest_source:
tbz x16, IND_SOURCE_BIT, .Ltest_indirection

/* Invalidate dest page to PoC. */
- mov x0, x13
- add x20, x0, #PAGE_SIZE
+ mov x2, x13
+ add x20, x2, #PAGE_SIZE
sub x1, x15, #1
- bic x0, x0, x1
-2: dc ivac, x0
- add x0, x0, x15
- cmp x0, x20
+ bic x2, x2, x1
+2: dc ivac, x2
+ add x2, x2, x15
+ cmp x2, x20
b.lo 2b
dsb sy

- mov x20, x13
- mov x21, x12
- copy_page x20, x21, x0, x1, x2, x3, x4, x5, x6, x7
-
- /* dest += PAGE_SIZE */
- add x13, x13, PAGE_SIZE
+ copy_page x13, x12, x1, x2, x3, x4, x5, x6, x7, x8
b .Lnext
-
.Ltest_indirection:
tbz x16, IND_INDIRECTION_BIT, .Ltest_destination
-
- /* ptr = addr */
- mov x14, x12
+ mov x14, x12 /* ptr = addr */
b .Lnext
-
.Ltest_destination:
tbz x16, IND_DESTINATION_BIT, .Lnext
-
- /* dest = addr */
- mov x13, x12
-
+ mov x13, x12 /* dest = addr */
.Lnext:
- /* entry = *ptr++ */
- ldr x16, [x14], #8
-
- /* while (!(entry & DONE)) */
- tbz x16, IND_DONE_BIT, .Lloop
-
+ ldr x16, [x14], #8 /* entry = *ptr++ */
+ tbz x16, IND_DONE_BIT, .Lloop /* while (!(entry & DONE)) */
.Ldone:
/* wait for writes from copy_page to finish */
dsb nsh
@@ -105,18 +77,16 @@ ENTRY(arm64_relocate_new_kernel)
isb

/* Start new image. */
- mov x0, x18
- mov x1, xzr
- mov x2, xzr
- mov x3, xzr
- br x17
-
-ENDPROC(arm64_relocate_new_kernel)
+ ldr x4, [x0, #KRELOC_ENTRY_ADDR] /* x4 = kimage_start */
+ ldr x3, [x0, #KRELOC_KERN_ARG3]
+ ldr x2, [x0, #KRELOC_KERN_ARG2]
+ ldr x1, [x0, #KRELOC_KERN_ARG1]
+ ldr x0, [x0, #KRELOC_KERN_ARG0] /* x0 = dtb address */
+ br x4
+END(arm64_relocate_new_kernel)

.ltorg
-
.align 3 /* To keep the 64-bit values below naturally aligned. */
-
.Lcopy_end:
.org KEXEC_CONTROL_PAGE_SIZE

--
2.23.0