releases/3.2.98/kaiser-use-alternative-instead-of-x86_cr3_pcid_noflush.patch

From: Hugh Dickins <hughd@google.com>
Date: Tue, 3 Oct 2017 20:49:04 -0700
Subject: kaiser: use ALTERNATIVE instead of x86_cr3_pcid_noflush

Now that we're playing the ALTERNATIVE game, use that more efficient
method: instead of user-mapping an extra page, and reading an extra
cacheline each time for x86_cr3_pcid_noflush.

Neel has found that __stringify(bts $X86_CR3_PCID_NOFLUSH_BIT, %rax)
is a working substitute for the "bts $63, %rax" in these ALTERNATIVEs;
but the one line with $63 in looks clearer, so let's stick with that.

Worried about what happens with an ALTERNATIVE between the jump and
jump label in another ALTERNATIVE?  I was, but have checked the
combinations in SWITCH_KERNEL_CR3_NO_STACK at entry_SYSCALL_64,
and it does a good job.

(cherry picked from Change-Id: I46d06167615aa8d628eed9972125ab2faca93f05)

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 arch/x86/include/asm/kaiser.h |  6 +++---
 arch/x86/kernel/entry_64.S    |  3 ++-
 arch/x86/mm/kaiser.c          | 10 +---------
 3 files changed, 6 insertions(+), 13 deletions(-)

--- a/arch/x86/include/asm/kaiser.h
+++ b/arch/x86/include/asm/kaiser.h
@@ -25,7 +25,8 @@
 .macro _SWITCH_TO_KERNEL_CR3 reg
 movq %cr3, \reg
 andq $(~(X86_CR3_PCID_ASID_MASK | KAISER_SHADOW_PGD_OFFSET)), \reg
-orq  x86_cr3_pcid_noflush, \reg
+/* If PCID enabled, set X86_CR3_PCID_NOFLUSH_BIT */
+ALTERNATIVE "", "bts $63, \reg", X86_FEATURE_PCID
 movq \reg, %cr3
 .endm
 
@@ -39,7 +40,7 @@ movq \reg, %cr3
 movq %cr3, \reg
 orq  PER_CPU_VAR(x86_cr3_pcid_user), \reg
 js   9f
-/* FLUSH this time, reset to NOFLUSH for next time (if PCID enabled) */
+/* If PCID enabled, FLUSH this time, reset to NOFLUSH for next time */
 movb \regb, PER_CPU_VAR(x86_cr3_pcid_user+7)
 9:
 movq \reg, %cr3
@@ -90,7 +91,6 @@ movq PER_CPU_VAR(unsafe_stack_register_b
 */
 DECLARE_PER_CPU_USER_MAPPED(unsigned long, unsafe_stack_register_backup);
 
-extern unsigned long x86_cr3_pcid_noflush;
 DECLARE_PER_CPU(unsigned long, x86_cr3_pcid_user);
 
 extern char __per_cpu_user_mapped_start[], __per_cpu_user_mapped_end[];
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -411,7 +411,8 @@ ENTRY(save_paranoid)
 	jz	2f
 	orl	$2, %ebx
 	andq	$(~(X86_CR3_PCID_ASID_MASK | KAISER_SHADOW_PGD_OFFSET)), %rax
-	orq	x86_cr3_pcid_noflush, %rax
+	/* If PCID enabled, set X86_CR3_PCID_NOFLUSH_BIT */
+	ALTERNATIVE "", "bts $63, %rax", X86_FEATURE_PCID
 	movq	%rax, %cr3
 2:
 #endif
--- a/arch/x86/mm/kaiser.c
+++ b/arch/x86/mm/kaiser.c
@@ -35,7 +35,6 @@ DEFINE_PER_CPU_USER_MAPPED(unsigned long
  * This is also handy because systems that do not support PCIDs
  * just end up or'ing a 0 into their CR3, which does no harm.
  */
-unsigned long x86_cr3_pcid_noflush __read_mostly;
 DEFINE_PER_CPU(unsigned long, x86_cr3_pcid_user);
 
 /*
@@ -349,9 +348,6 @@ void __init kaiser_init(void)
 				  __PAGE_KERNEL_VVAR);
 	kaiser_add_user_map_early((void *)VSYSCALL_START, PAGE_SIZE,
 				  vsyscall_pgprot);
-	kaiser_add_user_map_early(&x86_cr3_pcid_noflush,
-				  sizeof(x86_cr3_pcid_noflush),
-				  __PAGE_KERNEL);
 }
 
 /* Add a mapping to the shadow mapping, and synchronize the mappings */
@@ -423,18 +419,14 @@ pgd_t kaiser_set_shadow_pgd(pgd_t *pgdp,
 
 void kaiser_setup_pcid(void)
 {
-	unsigned long kern_cr3 = 0;
 	unsigned long user_cr3 = KAISER_SHADOW_PGD_OFFSET;
 
-	if (this_cpu_has(X86_FEATURE_PCID)) {
-		kern_cr3 |= X86_CR3_PCID_KERN_NOFLUSH;
+	if (this_cpu_has(X86_FEATURE_PCID))
 		user_cr3 |= X86_CR3_PCID_USER_NOFLUSH;
-	}
 	/*
 	 * These variables are used by the entry/exit
 	 * code to change PCID and pgd and TLB flushing.
 	 */
-	x86_cr3_pcid_noflush = kern_cr3;
 	this_cpu_write(x86_cr3_pcid_user, user_cr3);
 }