linux-kernel - Re: [PATCH v3 1/1] x86/fred: Fix INT80 emulation for FRED

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Date: Wed, 17 Apr 2024 08:06:31 -0700
From: Xin Li <xin@...or.com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, luto@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com
Subject: Re: [PATCH v3 1/1] x86/fred: Fix INT80 emulation for FRED

On 4/17/2024 2:38 AM, Borislav Petkov wrote:
> On Tue, Apr 16, 2024 at 11:30:01PM -0700, Xin Li (Intel) wrote:
>> 3) The FRED kernel entry handler does *NOT* dispatch INT instructions,
>>     which is of event type EVENT_TYPE_SWINT, so compared with
>>     do_int80_emulation(), there is no need to do any user mode check.
> 
> What does that mean?
> 
> An event handler doesn't dispatch INT insns?
> 
> /me is confused.
> 

Maybe better to say?

The FRED kernel entry handler fred_entry_from_kernel() calls 
fred_bad_type() if an event is of type EVENT_TYPE_SWINT because Kernel 
does not use INT insns! So if the kernel is handling an INT insn, it can 
only be from a user level application.


>> + * A dedicated FRED INT80 handler duplicates quite a bit of the code in
>> + * do_int80_emulation(), but it avoids sprinkling more tests and seems
>> + * more readable. Just remember that we can always unify common stuff
>> + * later if it turns out that it won't diverge anymore, i.e., after the
>> + * FRED code settles.
>> + */
> 
> And this is talking about duplication above and that text is duplicated
> from the commit message. :)

I wanted to keep it as a TODO.  I can remove it in the next iteration.

> 
> I'll zap it when applying.
> 
> Thx.
>