linux-kernel - Re: [PATCH v1 1/1] x86/fred: Fix int80 emulation for FRED

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Message-ID: <20240416101147.GDZh5O473e4X_ZG1lZ@fat_crate.local>
Date: Tue, 16 Apr 2024 12:11:47 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Xin Li (Intel)" <xin@...or.com>
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 v1 1/1] x86/fred: Fix int80 emulation for FRED

On Fri, Apr 12, 2024 at 04:40:58PM -0700, Xin Li (Intel) wrote:
> Commit 55617fb991df

Use the full commit abbreviation when mentioning commits:

"Commit

  55617fb991df ("x86/entry: Do not allow external 0x80 interrupts")

.."

> added a bunch of tests to the int $0x80 path,

Added a bunch of tests?

What does that even mean?

> however they are unnecessary and event wrong in fact under FRED.

Are the bunch of tests wrong or is do_int80_emulation() simply the wrong
handler to use on a FRED?

> First FRED distinguishes external interrupts from software interrupts,
> thus int80_emulation() should NEVER be called for handling an external
> interrupt, and then int80_is_external() should be skipped under FRED.
> 
> Second, the FRED kernel entry handler NEVER dispatches INTx, which is
> of event type EVENT_TYPE_SWINT, so the user mode checking in
> do_int80_emulation() is redundant, and should be skipped.
> 
> It might be even better to strip down do_int80_emulation() to a lean
> fred_int80_emulation(), not to mention int80_emulation() does a
> CLEAR_BRANCH_HISTORY.

Yah, how about you do a FRED-specific INT80 handler instead of
sprinkling moar tests around? fred_intx() looks like the right place to
stuff it in...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette