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>

diff --git a/arch/x86/include/asm/kaiser.h b/arch/x86/include/asm/kaiser.h
index 2fe06d0..704d9d6 100644 (file)
--- 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_backup), %rax
 */
 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[];

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index eb6c31b..81049db 100644 (file)
--- 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

diff --git a/arch/x86/mm/kaiser.c b/arch/x86/mm/kaiser.c
index f479fd8..5033206 100644 (file)
--- a/arch/x86/mm/kaiser.c
+++ b/arch/x86/mm/kaiser.c
@@ -35,7 +35,6 @@ DEFINE_PER_CPU_USER_MAPPED(unsigned long, unsafe_stack_register_backup);
  * 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, pgd_t pgd)
 
 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);
 }