linux-kernel - Re: [PATCH 2/2] x86,entry: Use PUSH_AND_CLEAR

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Date:   Wed, 20 Apr 2022 12:29:41 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     X86 ML <x86@...nel.org>, Josh Poimboeuf <jpoimboe@...hat.com>,
        Brian Gerst <brgerst@...il.com>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] x86,entry: Use PUSH_AND_CLEAR_REGS for compat

On Wed, Apr 20, 2022 at 4:53 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> Since the upper regs don't exist for ia32 code, preserving them
> doesn't hurt and it simplifies the code.

In entry_INT80_compat(), the upper regs need to be preserved on the
stack which makes the code identical to the macro idtentry except the
special prolog.

So reusing idtentry simplifiers more.

I don't ask to remove the change to entry_INT80_compat().

But I don't think the change to entry_INT80_compat()
fit the changelog.

I think it is better to split this patch into two.

The first one contains the change to entry_SYSENTER_compat()
and entry_SYSCALL_compat() with current changelog.

The second one contains the change to entry_INT80_compat()
and PUSH_AND_CLEAR_REGS with changelog saying it simplifies
entry_SYSENTER_compat().

My patchset can do the simplification by using idtentry
and remove save_rdi from PUSH_AND_CLEAR_REGS on top of it.

Thanks
Lai