[tip: x86/boot] x86/kexec: Drop page_list argument from relocate_kernel()

From: tip-bot2 for David Woodhouse
Date: Fri Dec 06 2024 - 05:20:16 EST

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The following commit has been merged into the x86/boot branch of tip:

Commit-ID: b3adabae8a96fee62184f4236bf60313b35244e9
Gitweb: https://git.kernel.org/tip/b3adabae8a96fee62184f4236bf60313b35244e9
Author: David Woodhouse <dwmw@xxxxxxxxxxxx>
AuthorDate: Thu, 05 Dec 2024 15:05:16
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Fri, 06 Dec 2024 10:42:00 +01:00

x86/kexec: Drop page_list argument from relocate_kernel()

The kernel's virtual mapping of the relocate_kernel page currently needs
to be RWX because it is written to before the %cr3 switch.

Now that the relocate_kernel page has its own .data section and local
variables, it can also have *global* variables. So eliminate the separate
page_list argument, and write the same information directly to variables
in the relocate_kernel page instead. This way, the relocate_kernel code
itself doesn't need to copy it.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Link: https://lore.kernel.org/r/20241205153343.3275139-11-dwmw2@xxxxxxxxxxxxx
---
arch/x86/include/asm/kexec.h | 12 +++------
arch/x86/kernel/machine_kexec_64.c | 18 +++++---------
arch/x86/kernel/relocate_kernel_64.S | 36 +++++++++------------------
3 files changed, 24 insertions(+), 42 deletions(-)

diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
index ccb8ff3..48e4f44 100644
--- a/arch/x86/include/asm/kexec.h
+++ b/arch/x86/include/asm/kexec.h
@@ -8,12 +8,6 @@
# define PA_PGD 2
# define PA_SWAP_PAGE 3
# define PAGES_NR 4
-#else
-# define PA_CONTROL_PAGE 0
-# define VA_CONTROL_PAGE 1
-# define PA_TABLE_PAGE 2
-# define PA_SWAP_PAGE 3
-# define PAGES_NR 4
#endif

# define KEXEC_CONTROL_PAGE_SIZE 4096
@@ -60,6 +54,10 @@ struct kimage;

/* The native architecture */
# define KEXEC_ARCH KEXEC_ARCH_X86_64
+
+extern unsigned long kexec_va_control_page;
+extern unsigned long kexec_pa_table_page;
+extern unsigned long kexec_pa_swap_page;
#endif

/*
@@ -122,7 +120,7 @@ relocate_kernel(unsigned long indirection_page,
#else
unsigned long
relocate_kernel(unsigned long indirection_page,
- unsigned long page_list,
+ unsigned long pa_control_page,
unsigned long start_address,
unsigned int preserve_context,
unsigned int host_mem_enc_active);
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 63dca5c..c9fd60f 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -315,6 +315,11 @@ int machine_kexec_prepare(struct kimage *image)
result = init_pgtable(image, __pa(control_page));
if (result)
return result;
+ kexec_va_control_page = (unsigned long)control_page;
+ kexec_pa_table_page = (unsigned long)__pa(image->arch.pgd);
+
+ if (image->type == KEXEC_TYPE_DEFAULT)
+ kexec_pa_swap_page = page_to_pfn(image->swap_page) << PAGE_SHIFT;

__memcpy(control_page, __relocate_kernel_start, reloc_end - reloc_start);

@@ -339,12 +344,11 @@ void machine_kexec_cleanup(struct kimage *image)
void machine_kexec(struct kimage *image)
{
unsigned long (*relocate_kernel_ptr)(unsigned long indirection_page,
- unsigned long page_list,
+ unsigned long pa_control_page,
unsigned long start_address,
unsigned int preserve_context,
unsigned int host_mem_enc_active);
unsigned long reloc_start = (unsigned long)__relocate_kernel_start;
- unsigned long page_list[PAGES_NR];
unsigned int host_mem_enc_active;
int save_ftrace_enabled;
void *control_page;
@@ -382,14 +386,6 @@ void machine_kexec(struct kimage *image)

control_page = page_address(image->control_code_page);

- page_list[PA_CONTROL_PAGE] = virt_to_phys(control_page);
- page_list[VA_CONTROL_PAGE] = (unsigned long)control_page;
- page_list[PA_TABLE_PAGE] = (unsigned long)__pa(image->arch.pgd);
-
- if (image->type == KEXEC_TYPE_DEFAULT)
- page_list[PA_SWAP_PAGE] = (page_to_pfn(image->swap_page)
- << PAGE_SHIFT);
-
/*
* Allow for the possibility that relocate_kernel might not be at
* the very start of the page.
@@ -417,7 +413,7 @@ void machine_kexec(struct kimage *image)

/* now call it */
image->start = relocate_kernel_ptr((unsigned long)image->head,
- (unsigned long)page_list,
+ virt_to_phys(control_page),
image->start,
image->preserve_context,
host_mem_enc_active);
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index f13866a..d52c3bb 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -34,9 +34,9 @@ SYM_DATA_LOCAL(saved_cr0, .quad 0)
SYM_DATA_LOCAL(saved_cr3, .quad 0)
SYM_DATA_LOCAL(saved_cr4, .quad 0)
/* other data */
-SYM_DATA_LOCAL(va_control_page, .quad 0)
-SYM_DATA_LOCAL(pa_table_page, .quad 0)
-SYM_DATA_LOCAL(pa_swap_page, .quad 0)
+SYM_DATA(kexec_va_control_page, .quad 0)
+SYM_DATA(kexec_pa_table_page, .quad 0)
+SYM_DATA(kexec_pa_swap_page, .quad 0)
SYM_DATA_LOCAL(pa_backup_pages_map, .quad 0)

.section .text.relocate_kernel,"ax";
@@ -46,7 +46,7 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
ANNOTATE_NOENDBR
/*
* %rdi indirection_page
- * %rsi page_list
+ * %rsi pa_control_page
* %rdx start address
* %rcx preserve_context
* %r8 host_mem_enc_active
@@ -79,31 +79,19 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
/* Save SME active flag */
movq %r8, %r12

- /*
- * get physical and virtual address of control page now
- * this is impossible after page table switch
- */
- movq PTR(PA_CONTROL_PAGE)(%rsi), %r8
- movq PTR(VA_CONTROL_PAGE)(%rsi), %r11
-
- /* get physical address of page table now too */
- movq PTR(PA_TABLE_PAGE)(%rsi), %r9
-
- /* get physical address of swap page now */
- movq PTR(PA_SWAP_PAGE)(%rsi), %r10
-
- /* save some information for jumping back */
- movq %r9, pa_table_page(%rip)
- movq %r10, pa_swap_page(%rip)
+ /* save indirection list for jumping back */
movq %rdi, pa_backup_pages_map(%rip)
- movq %r11, va_control_page(%rip)

/* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */
movq %rcx, %r11

/* Switch to the identity mapped page tables */
+ movq kexec_pa_table_page(%rip), %r9
movq %r9, %cr3

+ /* Physical address of control page */
+ movq %rsi, %r8
+
/* setup a new stack at the end of the physical control page */
lea PAGE_SIZE(%r8), %rsp

@@ -227,13 +215,13 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
/* get the re-entry point of the peer system */
movq 0(%rsp), %rbp
leaq relocate_kernel(%rip), %r8
- movq pa_swap_page(%rip), %r10
+ movq kexec_pa_swap_page(%rip), %r10
movq pa_backup_pages_map(%rip), %rdi
- movq pa_table_page(%rip), %rax
+ movq kexec_pa_table_page(%rip), %rax
movq %rax, %cr3
lea PAGE_SIZE(%r8), %rsp
call swap_pages
- movq va_control_page(%rip), %rax
+ movq kexec_va_control_page(%rip), %rax
addq $(virtual_mapped - relocate_kernel), %rax
pushq %rax
ANNOTATE_UNRET_SAFE

Next message: Dmitry Baryshkov: "[PATCH v6 00/10] drm: add DRM HDMI Codec framework"
Previous message: tip-bot2 for David Woodhouse: "[tip: x86/boot] x86/kexec: Eliminate writes through kernel mapping of relocate_kernel page"
In reply to: David Woodhouse: "[PATCH v5 10/20] x86/kexec: Drop page_list argument from relocate_kernel()"
Next in thread: David Woodhouse: "[PATCH v5 16/20] x86/kexec: Debugging support: Load an IDT and basic exception entry points"
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