Messages in this thread | | | Subject | Re: [PATCH 2/6] __wr_after_init: write rare for static allocation | From | Igor Stoppa <> | Date | Mon, 10 Dec 2018 00:22:56 +0200 |
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On 06/12/2018 06:44, Matthew Wilcox wrote: > On Tue, Dec 04, 2018 at 02:18:01PM +0200, Igor Stoppa wrote: >> +void *__wr_op(unsigned long dst, unsigned long src, __kernel_size_t len, >> + enum wr_op_type op) >> +{ >> + temporary_mm_state_t prev; >> + unsigned long flags; >> + unsigned long offset; >> + unsigned long wr_poking_addr; >> + >> + /* Confirm that the writable mapping exists. */ >> + BUG_ON(!wr_ready); >> + >> + if (WARN_ONCE(op >= WR_OPS_NUMBER, "Invalid WR operation.") || >> + WARN_ONCE(!is_wr_after_init(dst, len), "Invalid WR range.")) >> + return (void *)dst; >> + >> + offset = dst - (unsigned long)&__start_wr_after_init; >> + wr_poking_addr = wr_poking_base + offset; >> + local_irq_save(flags); > > Why not local_irq_disable()? Do we have a use-case for wanting to access > this from interrupt context?
No, not that I can think of. It was "just in case", but I can remove it.
>> + /* XXX make the verification optional? */ > > Well, yes. It seems like debug code to me.
Ok, I was not sure about this, because text_poke() does it as part of its normal operations.
>> + /* Randomize the poking address base*/ >> + wr_poking_base = TASK_UNMAPPED_BASE + >> + (kaslr_get_random_long("Write Rare Poking") & PAGE_MASK) % >> + (TASK_SIZE - (TASK_UNMAPPED_BASE + wr_range)); > > I don't think this is a great idea. We want to use the same mm for both > static and dynamic wr memory, yes? So we should have enough space for > all of ram, not splatter the static section all over the address space. > > On x86-64 (4 level page tables), we have a 64TB space for all of physmem > and 128TB of user space, so we can place the base anywhere in a 64TB > range.
I was actually wondering about the dynamic part. It's still not clear to me if it's possible to write the code in a sufficiently generic way that it could work on all 64 bit architectures. I'll start with x86-64 as you suggest.
-- igor
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