Joel Stanley [off-list ref] writes:

On Mon, Jan 8, 2018 at 8:54 AM, Michael Ellerman [off-list ref] wrote:

quoted

On some CPUs we can prevent the Meltdown vulnerability by flushing the
L1-D cache on exit from kernel to user mode, and from hypervisor to
guest.

Super minor nitpicks below. Don't let this hold up your work.

quoted

--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S

@@ -1449,6 +1449,88 @@ masked_##_H##interrupt:                                  \
        b       .;                                      \
        MASKED_DEC_HANDLER(_H)

+TRAMP_REAL_BEGIN(rfi_flush_fallback)
+       SET_SCRATCH0(r13);
+       GET_PACA(r13);
+       std     r9,PACA_EXRFI+EX_R9(r13)
+       std     r10,PACA_EXRFI+EX_R10(r13)
+       std     r11,PACA_EXRFI+EX_R11(r13)
+       std     r12,PACA_EXRFI+EX_R12(r13)
+       std     r8,PACA_EXRFI+EX_R13(r13)
+       mfctr   r9
+       ld      r10,PACA_RFI_FLUSH_FALLBACK_AREA(r13)
+       ld      r11,PACA_L1D_FLUSH_SETS(r13)
+       ld      r12,PACA_L1D_FLUSH_CONGRUENCE(r13)
+       /*
+        * The load adresses are at staggered offsets within cachelines,
+        * which suits some pipelines better (on others it should not
+        * hurt.

Nit: missing ) on the last line.

Thanks.

quoted

--- a/arch/powerpc/lib/feature-fixups.c
+++ b/arch/powerpc/lib/feature-fixups.c

@@ -116,6 +116,47 @@ void do_feature_fixups(unsigned long value, void *fixup_start, void *fixup_end)
        }
 }

+#ifdef CONFIG_PPC_BOOK3S_64
+void do_rfi_flush_fixups(enum l1d_flush_type types)
+{
+       unsigned int instrs[3], *dest;
+       long *start, *end;
+       int i;
+
+       start = PTRRELOC(&__start___rfi_flush_fixup),
+       end = PTRRELOC(&__stop___rfi_flush_fixup);
+
+       instrs[0] = 0x60000000; /* nop */
+       instrs[1] = 0x60000000; /* nop */
+       instrs[2] = 0x60000000; /* nop */
+
+       if (types & L1D_FLUSH_FALLBACK)

This looked a bit confusing on first read. Do we ever get
L1D_FLUSH_FALLBACK and the other types? If not, could it be made
clearer?

  if ( types & L1D_FLUSH_FALLBACK)
      /* stuff */
  else
    /* other types */

Yeah that would make more sense.

I'm going to merge it as-is because that's whats been tested, and given
the time of day I'm likely to break it if I try and refactor it. So we
can clean it up once it's merged.

cheers