linux-kernel - Re: [PATCH v3 06/21] x86/fpu/xstate: Calculate and remember dynamic xstate buffer sizes

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Date:   Wed, 3 Feb 2021 02:54:03 +0000
From:   "Bae, Chang Seok" <chang.seok.bae@...el.com>
To:     Borislav Petkov <bp@...e.de>
CC:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "Brown, Len" <len.brown@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Liu, Jing2" <jing2.liu@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 06/21] x86/fpu/xstate: Calculate and remember dynamic
 xstate buffer sizes

On Jan 27, 2021, at 01:38, Borislav Petkov <bp@...e.de> wrote:
> On Wed, Jan 27, 2021 at 01:23:35AM +0000, Bae, Chang Seok wrote:
>> Okay. I will prepare a separate cleanup patch that can be applied at the end
>> of the series. Will post the change in this thread at first.
> 
> No, this is not how this works. Imagine you pile up a patch at the end
> for each review feedback you've gotten. No, this will be an insane churn
> and an unreviewable mess.
> 
> What you do is you rework your patches like everyone else.

Yeah, it makes sense. I will post v4.

> Also, thinking about this more, I'm wondering if all those
> xstate-related attributes shouldn't be part of struct fpu instead of
> being scattered around like that.
> 
> That thing - struct fpu * - gets passed in everywhere anyway so all that
> min_size, max_size, ->xstate_ptr and whatever, looks like it wants to be
> part of struct fpu. Then maybe you won't need the accessors...

Well, min_size and max_size are not task-specific. So, it will be wasteful to
include in struct fpu.

I will follow your suggestion to add new helpers to access the size values,
instead of exporting them.

>>>> @@ -627,13 +627,18 @@ static void check_xstate_against_struct(int nr)
>>>> */
>>> 
>>> <-- There's a comment over this function that might need adjustment.
>> 
>> Do you mean an empty line? (Just want to clarify.)
> 
> No, I mean this comment:
> 
> * Dynamic XSAVE features allocate their own buffers and are not
> * covered by these checks. Only the size of the buffer for task->fpu
> * is checked here.
> 
> That probably needs adjusting as you do set min and max size here now
> for the dynamic buffer.

Oh, I see. Thank you.

>> Agreed. I will prepare a patch. At least will post the diff here.
> 
> You can send it separately from this patchset, ontop of current
> tip/master, so that I can take it now.

Posted, [1]. After all, the proposal is to remove the helper.

Thanks,
Chang

[1] https://lore.kernel.org/lkml/20210203024052.15789-1-chang.seok.bae@intel.com/