Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Peter Zijlstra <peterz@infradead.org>,
        Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc:     Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        "Guilherme G. Piccoli" <gpiccoli@igalia.com>,
        Steven Noonan <steven@uplinklabs.net>, kernel@collabora.com
Subject: Re: Direct rdtsc call side-effect
In-Reply-To: <20230601085602.GR4253@hirez.programming.kicks-ass.net>
References: <6719fb05-382c-8ec4-ccda-72798906a54b@collabora.com>
 <20230601085602.GR4253@hirez.programming.kicks-ass.net>
Date:   Thu, 01 Jun 2023 12:31:22 +0200
Message-ID: <87jzwneao5.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Thu, Jun 01 2023 at 10:56, Peter Zijlstra wrote:
> On Thu, Jun 01, 2023 at 01:45:35PM +0500, Muhammad Usama Anjum wrote:
>> We are thinking of saving and restoring the timestamp counter at suspend
>> and resume time respectively. In theory it can work on Intel because of
>> TSC_ADJUST register. But it'll never work on AMD until:
>> * AMD supports the same kind of adjust register. (AMD has said that the
>> adjust register cannot be implemented in their firmware. They'll have to
>> add it to their hardware.)
>> * by manual synchronization in kernel (I know you don't like this idea. But
>> there is something Windows is doing to save/restore and sync the TSC)
>
> Wine could set TIF_NOTSC, which will cause it to run with CR4.TSD
> cleared and cause RDTSC to #GP, at which point you can emulate it.

We should ask Microsoft to do the same. That'll fix the direct RDTSC
usage quickly. :)