Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Date:   Fri, 20 May 2022 14:58:19 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     Isaku Yamahata <isaku.yamahata@intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        frederic@kernel.org, paulmck@kernel.org, rjw@rjwysocki.net,
        x86@kernel.org, linux-kernel@vger.kernel.org, jpoimboe@kernel.org
Subject: Re: [RFC][PATCH 9/9] arch/idle: Change arch_cpu_idle() IRQ behaviour
Message-ID: <20220520125819.GS2578@worktop.programming.kicks-ass.net>
References: <20220519212750.656413111@infradead.org>
 <20220519213422.119695559@infradead.org>
 <20220519220349.GM2578@worktop.programming.kicks-ass.net>
 <20220520022052.mkrc4v4evtp74bxe@black.fi.intel.com>
 <20220520070614.GP2578@worktop.programming.kicks-ass.net>
 <20220520101322.flxf52mg6vkkbc7r@box.shutemov.name>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20220520101322.flxf52mg6vkkbc7r@box.shutemov.name>
Precedence: bulk

On Fri, May 20, 2022 at 01:13:22PM +0300, Kirill A. Shutemov wrote:

> So you want to call call the HLT hypercall with .irq_disabled=false and
> .do_sti=false, but actual RFLAGS.IF in the guest is 0 and avoid CLI on
> wake up expecting it to be cleared already, right?

Yep, just like MWAIT can, avoids pointless IF flipping.

> My reading of the spec is "don't do that". But actual behaviour is up to
> VMM and TDX module implementation. VMM doens't have access to the guest
> register file, so it *may* work, I donno.

Yeah, it totally *can* work, but I've no idea if they done the right
thing.