[Bug 293382] Dead lock and kernel crash around closefp_impl

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=293382

--- Comment #96 from Kyle Evans <kevans@freebsd.org> ---
(In reply to Alan Cox from comment #95)

AFAICT, they're very careful to avoid using it outside of hugetlb contexts. 
For example, they have this `invlpgb_kernel_range_flush` (which is maybe a
close analog for what the patch touches that calls `invlpgb_flush_addr_nosync`,
which uses a fixed `PTE_STRIDE`:

```
/* Flush addr, including globals, for all PCIDs. */
static inline void invlpgb_flush_addr_nosync(unsigned long addr, u16 nr)
{
        __invlpgb(0, 0, addr, nr, PTE_STRIDE, INVLPGB_FLAG_INCLUDE_GLOBAL);
}

/* Flush an arbitrarily large range of memory with INVLPGB. */
static void invlpgb_kernel_range_flush(struct flush_tlb_info *info)
{
        unsigned long addr, nr;

        for (addr = info->start; addr < info->end; addr += nr << PAGE_SHIFT) {
                nr = (info->end - addr) >> PAGE_SHIFT;

                /*
                 * INVLPGB has a limit on the size of ranges it can
                 * flush. Break up large flushes.
                 */
                nr = clamp_val(nr, 1, invlpgb_count_max);

                invlpgb_flush_addr_nosync(addr, nr);
        }
        __tlbsync();
}
```

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