Messages in this thread |  | | Date | Mon, 24 Feb 2014 09:27:46 -0800 | From | Dave Hansen <> | Subject | Re: [PATCH v5 2/3] x86, mpx: hook #BR exception handler to allocate bound tables |
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On 02/23/2014 05:27 AM, Qiaowei Ren wrote: > +static bool allocate_bt(unsigned long bd_entry) > +{ > + unsigned long bt_size = 1UL << (MPX_L2_BITS+MPX_L2_SHIFT); > + unsigned long bt_addr, old_val = 0; > + > + bt_addr = sys_mmap_pgoff(0, bt_size, PROT_READ | PROT_WRITE, > + MAP_ANONYMOUS | MAP_PRIVATE | MAP_POPULATE, -1, 0); > + if (bt_addr == -1) { > + pr_err("L2 Node Allocation Failed at L1 addr %lx\n", > + bd_entry); > + return false; > + } > + bt_addr = (bt_addr & MPX_L2_NODE_ADDR_MASK) | 0x01; > + > + user_atomic_cmpxchg_inatomic(&old_val, > + (long __user *)bd_entry, 0, bt_addr); > + if (old_val) > + vm_munmap(bt_addr & MPX_L2_NODE_ADDR_MASK, bt_size); > + > + return true; > +} > + > +bool do_mpx_bt_fault(struct xsave_struct *xsave_buf) > +{ > + unsigned long status; > + unsigned long bd_entry, bd_base; > + unsigned long bd_size = 1UL << (MPX_L1_BITS+MPX_L1_SHIFT); > + > + bd_base = xsave_buf->bndcsr.cfg_reg_u & MPX_BNDCFG_ADDR_MASK; > + status = xsave_buf->bndcsr.status_reg; > + > + bd_entry = status & MPX_BNDSTA_ADDR_MASK; > + if ((bd_entry >= bd_base) && (bd_entry < bd_base + bd_size)) > + return allocate_bt(bd_entry); > + > + return false; > +}
Can you talk a little bit about what the design is here? Why does the kernel have to do the allocation of the virtual address space? Does it really need to MAP_POPULATE? bt_size looks like 4MB, and that's an awful lot of memory to eat up at once. Shouldn't we just let the kernel demand-fault this like everything else?
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