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Subject[PATCH 2/2] x86/entry: always flush user CR3 in RESTORE_CR3
Date
RESTORE_CR3 is called when CPL==0 or #DF, it is unlikely
CPL==0&cr3==userCR3 and #DF itself is unlikely case.
There is no much overhead to always flush userCR3.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/entry/calling.h | 27 ++++++---------------------
arch/x86/entry/entry_64.S | 6 +++---
2 files changed, 9 insertions(+), 24 deletions(-)

diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 505246185624..ff26e4eb7063 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -265,33 +265,18 @@ For 32-bit we have the following conventions - kernel is built with
.Ldone_\@:
.endm

-.macro RESTORE_CR3 scratch_reg:req save_reg:req
+.macro RESTORE_CR3 save_reg:req
ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI

/*
* Skip resuming KERNEL pages since it is already KERNEL CR3.
+ *
+ * RESTORE_CR3 is called when CPL==0 or #DF, it is unlikely
+ * CPL==0&cr3==userCR3 and #DF itself is unlikely case.
+ * There is no much overhead to always flush userCR3.
*/
bt $PTI_USER_PGTABLE_BIT, \save_reg
jnc .Lend_\@
-
- ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID
-
- /*
- * Check if there's a pending flush for the user ASID we're
- * about to set.
- */
- movq \save_reg, \scratch_reg
- andq $(0x7FF), \scratch_reg
- bt \scratch_reg, THIS_CPU_user_pcid_flush_mask
- jnc .Lnoflush_\@
-
- btr \scratch_reg, THIS_CPU_user_pcid_flush_mask
- jmp .Lwrcr3_\@
-
-.Lnoflush_\@:
- SET_NOFLUSH_BIT \save_reg
-
-.Lwrcr3_\@:
movq \save_reg, %cr3
.Lend_\@:
.endm
@@ -306,7 +291,7 @@ For 32-bit we have the following conventions - kernel is built with
.endm
.macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req
.endm
-.macro RESTORE_CR3 scratch_reg:req save_reg:req
+.macro RESTORE_CR3 save_reg:req
.endm

#endif
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index d983a0d4bc73..46efa842a45e 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1283,13 +1283,13 @@ SYM_CODE_START_LOCAL(paranoid_exit)
jnz .Lparanoid_exit_no_swapgs
TRACE_IRQS_IRETQ
/* Always restore stashed CR3 value (see paranoid_entry) */
- RESTORE_CR3 scratch_reg=%rbx save_reg=%r14
+ RESTORE_CR3 save_reg=%r14
SWAPGS_UNSAFE_STACK
jmp restore_regs_and_return_to_kernel
.Lparanoid_exit_no_swapgs:
TRACE_IRQS_IRETQ_DEBUG
/* Always restore stashed CR3 value (see paranoid_entry) */
- RESTORE_CR3 scratch_reg=%rbx save_reg=%r14
+ RESTORE_CR3 save_reg=%r14
jmp restore_regs_and_return_to_kernel
SYM_CODE_END(paranoid_exit)

@@ -1703,7 +1703,7 @@ end_repeat_nmi:
call exc_nmi

/* Always restore stashed CR3 value (see paranoid_entry) */
- RESTORE_CR3 scratch_reg=%r15 save_reg=%r14
+ RESTORE_CR3 save_reg=%r14

testl %ebx, %ebx /* swapgs needed? */
jnz nmi_restore
--
2.20.1
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