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Subject[PATCH 1/2] x86/entry: Don't write to CR3 when restoring to kernel CR3
Date
Skip resuming KERNEL pages since it is already KERNEL CR3

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/entry/calling.h | 13 ++++---------
1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 1c7f13bb6728..505246185624 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -268,14 +268,13 @@ For 32-bit we have the following conventions - kernel is built with
.macro RESTORE_CR3 scratch_reg:req save_reg:req
ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI

- ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID
-
/*
- * KERNEL pages can always resume with NOFLUSH as we do
- * explicit flushes.
+ * Skip resuming KERNEL pages since it is already KERNEL CR3.
*/
bt $PTI_USER_PGTABLE_BIT, \save_reg
- jnc .Lnoflush_\@
+ jnc .Lend_\@
+
+ ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID

/*
* Check if there's a pending flush for the user ASID we're
@@ -293,10 +292,6 @@ For 32-bit we have the following conventions - kernel is built with
SET_NOFLUSH_BIT \save_reg

.Lwrcr3_\@:
- /*
- * The CR3 write could be avoided when not changing its value,
- * but would require a CR3 read *and* a scratch register.
- */
movq \save_reg, %cr3
.Lend_\@:
.endm
--
2.20.1
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