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    SubjectRe: [PATCH 07/11] powerpc/64s: Add support for RFI flush of L1-D cache
    On Mon, Jan 8, 2018 at 8:54 AM, Michael Ellerman <mpe@ellerman.id.au> wrote:
    > 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.

    > --- 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.

    > + */
    > + addi r12,r12,8
    > + mtctr r11
    > + DCBT_STOP_ALL_STREAM_IDS(r11) /* Stop prefetch streams */
    > +

    > --- 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 */


    > + /* b .+16 to fallback flush */
    > + instrs[0] = 0x48000010;
    > +
    > + i = 0;
    > + if (types & L1D_FLUSH_ORI) {
    > + instrs[i++] = 0x63ff0000; /* ori 31,31,0 speculation barrier */
    > + instrs[i++] = 0x63de0000; /* ori 30,30,0 L1d flush*/
    > + }
    > +
    > + if (types & L1D_FLUSH_MTTRIG)
    > + instrs[i++] = 0x7c12dba6; /* mtspr TRIG2,r0 (SPR #882) */
    > +
    > + for (i = 0; start < end; start++, i++) {
    > + dest = (void *)start + *start;
    > +
    > + pr_devel("patching dest %lx\n", (unsigned long)dest);
    > +
    > + patch_instruction(dest, instrs[0]);
    > + patch_instruction(dest + 1, instrs[1]);
    > + patch_instruction(dest + 2, instrs[2]);
    > + }
    > +
    > + printk(KERN_DEBUG "rfi-flush: patched %d locations\n", i);
    > +}
    > +#endif /* CONFIG_PPC_BOOK3S_64 */
    > +
    > void do_lwsync_fixups(unsigned long value, void *fixup_start, void *fixup_end)
    > {
    > long *start, *end;
    > --
    > 2.14.3
    >

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