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Message-ID: <1fbb0c1a-998f-4424-82aa-12483fafb197@zytor.com>
Date: Mon, 15 Apr 2024 09:21:00 -0700
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Subject: Re: [PATCH v1 1/1] x86/fred: Fix int80 emulation for FRED
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To: "Xin Li (Intel)" <xin@zytor.com>, linux-kernel@vger.kernel.org
Cc: luto@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, x86@kernel.org
References: <20240412234058.1106744-1-xin@zytor.com>
From: "H. Peter Anvin" <hpa@zytor.com>
In-Reply-To: <20240412234058.1106744-1-xin@zytor.com>
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On 4/12/24 16:40, Xin Li (Intel) wrote:
> Commit 55617fb991df added a bunch of tests to the int $0x80 path, however
> they are unnecessary and event wrong in fact under 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.
> 
> Suggested-by: H. Peter Anvin (Intel) <hpa@zytor.com>
> Signed-off-by: Xin Li (Intel) <xin@zytor.com>
> ---
>   arch/x86/entry/common.c | 22 ++++++++++++++++++++--
>   1 file changed, 20 insertions(+), 2 deletions(-)

Note: this is the minimal bug fix versions and belongs in x86/urgent.

	-hpa