On Wed, 22 Apr 2020 at 05:33, Richard Henderson
<richard.hender...@linaro.org> wrote:
>
> With sve_cont_ldst_pages, the differences between first-fault and no-fault
> are minimal, so unify the routines. With cpu_probe_watchpoint, we are able
> to make progress through pages with TLB_WATCHPOINT set when the watchpoint
> does not actually fire.
>
> Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
> /*
> - * Perform one normal read, which will fault or not.
> - * But it is likely to bring the page into the tlb.
> + * From this point on, all memory operations are MemSingleNF.
> + *
> + * Per the MemSingleNF pseudocode, a no-fault load from Device memory
> + * must not actually hit the bus -- it returns (UNKNOWN, FAULT) instead.
> + * If you map non-RAM with Normal memory attributes and do a NF
> + * load then it should access the bus -- but doing so is illegal.
> + *
> + * While we do not have access to the memory attributes from the PTE
> + * to tell Device memory from Normal memory, we can validly assume that
> + * non-RAM has been mapped as Device memory. Thus we indicate fault
> + * on all MMIO.
I still don't understand why this is right. All non-RAM is MMIO
but not all MMIO is non-RAM; so you might have something that's
MMIO (at least for the moment) and has been mapped Normal. That
shouldn't fault.
> + *
> + * Similarly, CPU_BP breakpoints would raise exceptions, and so
> + * return (UNKNOWN, FAULT). For simplicity, we consider gdb and
> + * architectural breakpoints the same.
> */
> - tlb_fn(env, vd, reg_off, addr + mem_off, retaddr);
> + if (unlikely(flags & TLB_MMIO)) {
> + goto do_fault;
> + }
thanks
-- PMM
