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Mon, 13 Apr 2026 15:31:35 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface MIME-Version: 1.0 X-ThreadId: AMdy4yCH1GcR Date: Mon, 13 Apr 2026 21:30:11 +0200 From: "Arnd Bergmann" To: "David Woodhouse" , "Thomas Gleixner" , LKML Cc: x86@kernel.org, "Baolu Lu" , iommu@lists.linux.dev, "Michael Grzeschik" , Netdev , linux-wireless@vger.kernel.org, "Herbert Xu" , linux-crypto@vger.kernel.org, "Vlastimil Babka (SUSE)" , linux-mm@kvack.org, "Bernie Thompson" , linux-fbdev@vger.kernel.org, "Theodore Ts'o" , linux-ext4@vger.kernel.org, "Andrew Morton" , "Uladzislau Rezki (Sony)" , "Marco Elver" , "Dmitry Vyukov" , kasan-dev@googlegroups.com, "Andrey Ryabinin" , "Thomas Sailer" , linux-hams@vger.kernel.org, "Jason A . Donenfeld" , "Richard Henderson" , linux-alpha@vger.kernel.org, "Russell King" , linux-arm-kernel@lists.infradead.org, "Catalin Marinas" , "Huacai Chen" , loongarch@lists.linux.dev, "Geert Uytterhoeven" , linux-m68k@lists.linux-m68k.org, "Dinh Nguyen" , "Jonas Bonn" , "linux-openrisc@vger.kernel.org" , "Helge Deller" , linux-parisc@vger.kernel.org, "Michael Ellerman" , linuxppc-dev@lists.ozlabs.org, "Paul Walmsley" , linux-riscv@lists.infradead.org, "Heiko Carstens" , linux-s390@vger.kernel.org, "David S . Miller" , sparclinux@vger.kernel.org Message-Id: <07df88e5-208d-4aac-9668-a3b0c65ae529@app.fastmail.com> In-Reply-To: <7a48b636cb3146f4f7134c6d4fe42070ac2edb43.camel@infradead.org> References: <20260410120044.031381086@kernel.org> <20260410120318.592237447@kernel.org> <7a48b636cb3146f4f7134c6d4fe42070ac2edb43.camel@infradead.org> Subject: Re: [patch 15/38] ptp: ptp_vmclock: Replace get_cycles() usage Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260413_123140_934086_B52A23AA X-CRM114-Status: GOOD ( 13.53 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Apr 13, 2026, at 17:33, David Woodhouse wrote: > On Fri, 2026-04-10 at 14:19 +0200, Thomas Gleixner wrote: > > ... depend on TSC_RELIABLE=C2=B9, since if the guest doesn't believe t= hat it > is, then the guest shouldn't be trying to use it as the basis for > precise timing. > > =C2=B9 (Or... one of the other zoo of TSC flags for the gradually redu= cing > brokenness over the years...) It looks like this is sufficiently handled in the caller: static int vmclock_get_crosststamp(struct vmclock_state *st, struct ptp_system_timestamp *sts, struct system_counterval_t *system_co= unter, struct timespec64 *tspec) { .... #ifdef CONFIG_X86 /* * We'd expect the hypervisor to know this and to report the clo= ck * status as VMCLOCK_STATUS_UNRELIABLE. But be paranoid. */ if (check_tsc_unstable()) return -EINVAL; #endif With 486 and ELAN out of the way, Winchip6 seems to be the only one without X86_FEATURE_TSC, so I think the next logical step would be to turn off Winchip6 as well and remove all X86_FEATURE_TSC and CONFIG_X86_TSC checks. Arnd