x86/mm: Optimize RESTORE_CR3

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>

diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 7894e5c..45a63e0 100644 (file)
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -281,8 +281,34 @@ For 32-bit we have the following conventions - kernel is built with
 .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 conventions - kernel is built with
 .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

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index fd50184..ed31d00 100644 (file)
--- 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