[PATCH 4.14 027/146] x86/mm: Optimize RESTORE_CR3

Greg Kroah-Hartman
2018-01-01T14:43:03Z

From: Peter Zijlstra <peterz@infradead.org>

commit 21e94459110252d41b45c0c8ba50fd72a664d50c upstream.

Most NMI/paranoid exceptions will not in fact change pagetables and would
thus not require TLB flushing, however RESTORE_CR3 uses flushing CR3
writes.

Restores to kernel PCIDs can be NOFLUSH, because we explicitly flush the
kernel mappings and now that we track which user PCIDs need flushing we can
avoid those too when possible.

This does mean RESTORE_CR3 needs an additional scratch_reg, luckily both
sites have plenty available.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/entry/calling.h | 30 ++++++++++++++++++++++++++++--
arch/x86/entry/entry_64.S | 4 ++--
2 files changed, 30 insertions(+), 4 deletions(-)

--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -281,8 +281,34 @@ For 32-bit we have the following convent
.Ldone_\@:
.endm

-.macro RESTORE_CR3 save_reg:req
+.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.
+ */
+ bt $X86_CR3_PTI_SWITCH_BIT, \save_reg
+ jnc .Lnoflush_\@
+
+ /*
+ * 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_\@:
/*
* The CR3 write could be avoided when not changing its value,
* but would require a CR3 read *and* a scratch register.
@@ -301,7 +327,7 @@ For 32-bit we have the following convent
.endm
.macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req
.endm
-.macro RESTORE_CR3 save_reg:req
+.macro RESTORE_CR3 scratch_reg:req save_reg:req
.endm

#endif
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1288,7 +1288,7 @@ ENTRY(paranoid_exit)
testl %ebx, %ebx /* swapgs needed? */
jnz .Lparanoid_exit_no_swapgs
TRACE_IRQS_IRETQ
- RESTORE_CR3 save_reg=%r14
+ RESTORE_CR3 scratch_reg=%rbx save_reg=%r14
SWAPGS_UNSAFE_STACK
jmp .Lparanoid_exit_restore
.Lparanoid_exit_no_swapgs:
@@ -1730,7 +1730,7 @@ end_repeat_nmi:
movq $-1, %rsi
call do_nmi

- RESTORE_CR3 save_reg=%r14
+ RESTORE_CR3 scratch_reg=%r15 save_reg=%r14

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