From: Joerg Roedel <jroedel@xxxxxxx> Restoring the segments can cause exceptions that need to be handled. With PTI enabled, we still need to be on kernel cr3 when the exception happens. For the cr3-switch we need at least one integer scratch register, so we can't switch with the user integer registers already loaded. Avoid a push/pop cycle to free a register for the cr3 switch by restoring the segments first. That way the integer registers are not live yet and we can use them for the cr3 switch. This also helps in the NMI path, where we need to leave with the same cr3 as we entered. There we still have the callee-saved registers live when switching cr3s. Signed-off-by: Joerg Roedel <jroedel@xxxxxxx> --- arch/x86/entry/entry_32.S | 50 ++++++++++++++++++++--------------------------- 1 file changed, 21 insertions(+), 29 deletions(-) diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 9bd7718..b39c5e2 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -92,11 +92,6 @@ .macro PUSH_GS pushl $0 .endm -.macro POP_GS pop=0 - addl $(4 + \pop), %esp -.endm -.macro POP_GS_EX -.endm /* all the rest are no-op */ .macro PTGS_TO_GS @@ -116,20 +111,6 @@ pushl %gs .endm -.macro POP_GS pop=0 -98: popl %gs - .if \pop <> 0 - add $\pop, %esp - .endif -.endm -.macro POP_GS_EX -.pushsection .fixup, "ax" -99: movl $0, (%esp) - jmp 98b -.popsection - _ASM_EXTABLE(98b, 99b) -.endm - .macro PTGS_TO_GS 98: mov PT_GS(%esp), %gs .endm @@ -201,24 +182,35 @@ popl %eax .endm -.macro RESTORE_REGS pop=0 - RESTORE_INT_REGS -1: popl %ds -2: popl %es -3: popl %fs - POP_GS \pop +.macro RESTORE_SEGMENTS +1: mov PT_DS(%esp), %ds +2: mov PT_ES(%esp), %es +3: mov PT_FS(%esp), %fs + PTGS_TO_GS .pushsection .fixup, "ax" -4: movl $0, (%esp) +4: movl $0, PT_DS(%esp) jmp 1b -5: movl $0, (%esp) +5: movl $0, PT_ES(%esp) jmp 2b -6: movl $0, (%esp) +6: movl $0, PT_FS(%esp) jmp 3b .popsection _ASM_EXTABLE(1b, 4b) _ASM_EXTABLE(2b, 5b) _ASM_EXTABLE(3b, 6b) - POP_GS_EX + PTGS_TO_GS_EX +.endm + +.macro RESTORE_SKIP_SEGMENTS pop=0 + /* Jump over the segments stored on stack */ + addl $((4 * 4) + \pop), %esp +.endm + +.macro RESTORE_REGS pop=0 + RESTORE_SEGMENTS + RESTORE_INT_REGS + /* Skip over already restored segment registers */ + RESTORE_SKIP_SEGMENTS \pop .endm .macro CHECK_AND_APPLY_ESPFIX -- 2.7.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
