linux-kernel - Re: [PATCH v2 27/39] x86/entry,xen: Early rewrite of restore_regs_and_return_to

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Date:   Thu, 24 Feb 2022 17:51:13 +0000
From:   Andrew Cooper <Andrew.Cooper3@...rix.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "joao@...rdrivepizza.com" <joao@...rdrivepizza.com>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "samitolvanen@...gle.com" <samitolvanen@...gle.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "alyssa.milburn@...el.com" <alyssa.milburn@...el.com>,
        "mbenes@...e.cz" <mbenes@...e.cz>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "mhiramat@...nel.org" <mhiramat@...nel.org>,
        "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>
Subject: Re: [PATCH v2 27/39] x86/entry,xen: Early rewrite of
 restore_regs_and_return_to_kernel()

On 24/02/2022 14:52, Peter Zijlstra wrote:
> By doing an early rewrite of 'jmp native_iret` in
> restore_regs_and_return_to_kernel() we can get rid of the last
> INTERRUPT_RETURN user and paravirt_iret.
>
> Suggested-by: Andrew Cooper <Andrew.Cooper3@...rix.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

As an observation, if you move this earlier in the series, you'll reduce
the churn by not needing to take out ENDBRs which you inserted previously.

Patches 25-27 all look like the can be prerequisites, ahead of patch 5.

~Andrew