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Thu, 09 Jul 2026 00:21:56 -0700 (PDT) Date: Thu, 9 Jul 2026 08:21:55 +0100 From: Matt Fleming To: Borislav Petkov Cc: Rik van Riel , Henrik =?utf-8?Q?B=C3=B6ving?= , dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, linux-kernel@vger.kernel.org, Sebastian Ullrich , Joscha Mennicken , kernel-team@cloudflare.com Subject: Re: PROBLEM: Probabilistic segfault on AMD hardware with INVLPGB Message-ID: References: <9363eca429424d967052bc401d4d835f1e6d2716.camel@surriel.com> <20260708161739.GAak54I-I0n5Pt_vAY@fat_crate.local> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260708161739.GAak54I-I0n5Pt_vAY@fat_crate.local> On Wed, Jul 08, 2026 at 09:17:39AM -0700, Borislav Petkov wrote: > Hey man, > > what's up? > > I see you're having fun. :-P Hey! Yep, you know me mate... slightest whiff of a CPU bug and I'm there ;-) > On Tue, Jul 07, 2026 at 01:18:30PM +0100, Matt Fleming wrote: > > Hi Rik and Henrik, > > > > I've got a small C reproducer that triggers this within the first round > > on Cloudflare's AMD Turin machines: > > > > https://gist.github.com/mfleming/ca26ad3f8d65a12d23d62fb176480fc1 > > > > Build: > > > > gcc -O2 -Wall -Wextra -pthread -static -o repro-invlpgb repro-invlpgb.c > > You need to have -std=c11 here on Debian-based systems because it says > > repro-invlpgb.c:94:30: error: implicit declaration of function ‘ATOMIC_VAR_INIT’; did you mean ‘ATOMIC_FLAG_INIT’? [-Wimplicit-function-declaration] > 94 | static atomic_bool running = ATOMIC_VAR_INIT(true); > > here due to not "seeing" the stdatomic.h include. I guess atomics are a C11 > thing... :) Thanks! I guess Ubuntu's GCC defaults masked this.