Messages in this thread | | | Date | Fri, 13 Aug 2021 12:04:43 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v9 08/26] x86/fpu/xstate: Introduce helpers to manage the XSTATE buffer dynamically |
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On Fri, Aug 13, 2021 at 08:04:54AM +0000, Bae, Chang Seok wrote: > Yes, each state offset in the non-compacted format is fixed in a machine > regardless of RFBM. So, simply take the size like that.
Comment above it please.
Also, why is this special case needed at all?
> But it might be better to simplify this hunk for readability. I > suspect its call sites are not that performance-critical.
That's *exactly* what I'm driving at!
> Every task’s state_mask should begin as aligned with the default buffer. > fpu_clone() sets this for all, except init_task. > Maybe: > “Make sure init_task’s state_mask aligned with its __default_state"
Why "make sure"?
There's nothing to make sure - it is simply so that initially, the FPU buffer used is the static one, without dynamic states. Just say that instead.
> How about enlarge_xstate_buffer() or realloc_xstate_buffer()?
realloc is fine along with a proper explanation above it why the realloc is done/needed.
> The query is intended to check whether the xstate buffer is fully expanded or > not -- no need to enlarge. > > If the buffer is already the maximum, the code to retrieve XSTATE_BV, this > call, etc should be skipped there. > > If the query is moved here, I guess this call site code becomes a bit ugly.
Why does it become ugly?
You simply return early without touching the buffer at all.
> No, it is still pointed by fpu->state and will be freed in the exit path.
Exit path of the task?
All I see is "return -ENOMEM" and no callers of alloc_xstate_buffer() are calling free_xstate_buffer()...
And looking further into the patchset:
exc_device_not_available does not call free_xstate_buffer() I'm assuming
force_sig_fault(SIGILL, ILL_ILLOPC,..
later will cause arch_release_task_struct() to happen which will call free_xstate_buffer(). Yes, no?
I don't see any freeing in xstateregs_set() either, so what's happening there when it returns -ENOMEM?
I guess there we remain with the old buffer, i.e., the ptrace operation fails.
Am I close?
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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