powerpc/32s: Speed up likely path of kuap_update_sr()

In most cases, kuap_update_sr() will update a single segment
register.

We know that first update will always be done, if there is no
segment register to update at all, kuap_update_sr() is not
called.

Avoid recurring calculations and tests in that case.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/848f18d213b8341939add7302dc4ef80cc7a12e3.1620307636.git.christophe.leroy@csgroup.eu

diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
index 1670dfe9d4f10bfd346eb01afd936861f32db057..c1f7c2e625a6564a4a13db5707e6a864b4ee9d53 100644 (file)
--- a/arch/powerpc/include/asm/book3s/32/kup.h
+++ b/arch/powerpc/include/asm/book3s/32/kup.h
@@ -15,11 +15,13 @@ static inline void kuap_update_sr(u32 sr, u32 addr, u32 end)
 {
        addr &= 0xf0000000;     /* align addr to start of segment */
        barrier();      /* make sure thread.kuap is updated before playing with SRs */
-       while (addr < end) {
+       for (;;) {
                mtsr(sr, addr);
+               addr += 0x10000000;     /* address of next segment */
+               if (addr >= end)
+                       break;
                sr += 0x111;            /* next VSID */
                sr &= 0xf0ffffff;       /* clear VSID overflow */
-               addr += 0x10000000;     /* address of next segment */
        }
        isync();        /* Context sync required after mtsr() */
 }