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x86/boot/compressed/64: Use page table in trampoline memory 

If a bootloader enables 64-bit mode with 4-level paging, we might need to
switch over to 5-level paging. The switching requires the disabling
paging. It works fine if kernel itself is loaded below 4G.

But if the bootloader put the kernel above 4G (i.e. in kexec() case),
we would lose control as soon as paging is disabled, because the code
becomes unreachable to the CPU.

To handle the situation, we need a trampoline in lower memory that would
take care of switching on 5-level paging.

Apart from the trampoline code itself we also need a place to store
top-level page table in lower memory as we don't have a way to load
64-bit values into CR3 in 32-bit mode. We only really need 8 bytes there
as we only use the very first entry of the page table. But we allocate a
whole page anyway.

This patch switches 32-bit code to use page table in trampoline memory.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20180312100246.89175-4-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Kirill A. Shutemov 2018-03-12 13:02:45 +03:00 committed by Ingo Molnar
parent f7ff53e470
commit 0a1756bd28
1 changed files with 23 additions and 24 deletions
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47
arch/x86/boot/compressed/head_64.S
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@ -336,23 +336,6 @@ ENTRY(startup_64)
/* Save the trampoline address in RCX */
movq %rax, %rcx
/* Check if we need to enable 5-level paging */
cmpq $0, %rdx
jz lvl5
/* Clear additional page table */
leaq lvl5_pgtable(%rbx), %rdi
xorq %rax, %rax
movq $(PAGE_SIZE/8), %rcx
rep stosq
/*
* Setup current CR3 as the first and only entry in a new top level
* page table.
*/
movq %cr3, %rdi
leaq 0x7 (%rdi), %rax
movq %rax, lvl5_pgtable(%rbx)
/* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */
pushq $__KERNEL32_CS
@ -524,13 +507,31 @@ compatible_mode:
btrl $X86_CR0_PG_BIT, %eax
movl %eax, %cr0
/* Point CR3 to 5-level paging */
leal lvl5_pgtable(%ebx), %eax
movl %eax, %cr3
/* Check what paging mode we want to be in after the trampoline */
cmpl $0, %edx
jz 1f
/* Enable PAE and LA57 mode */
/* We want 5-level paging: don't touch CR3 if it already points to 5-level page tables */
movl %cr4, %eax
orl $(X86_CR4_PAE | X86_CR4_LA57), %eax
testl $X86_CR4_LA57, %eax
jnz 3f
jmp 2f
1:
/* We want 4-level paging: don't touch CR3 if it already points to 4-level page tables */
movl %cr4, %eax
testl $X86_CR4_LA57, %eax
jz 3f
2:
/* Point CR3 to the trampoline's new top level page table */
leal TRAMPOLINE_32BIT_PGTABLE_OFFSET(%ecx), %eax
movl %eax, %cr3
3:
/* Enable PAE and LA57 (if required) paging modes */
movl $X86_CR4_PAE, %eax
cmpl $0, %edx
jz 1f
orl $X86_CR4_LA57, %eax
1:
movl %eax, %cr4
/* Calculate address we are running at */
@ -611,5 +612,3 @@ boot_stack_end:
.balign 4096
pgtable:
.fill BOOT_PGT_SIZE, 1, 0
lvl5_pgtable:
.fill PAGE_SIZE, 1, 0