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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4995ea27b29sm360281525e9.11.2026.08.10.03.06.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Aug 2026 03:06:31 -0700 (PDT) Date: Mon, 10 Aug 2026 11:06:24 +0100 From: David Laight To: Sergey Senozhatsky Cc: Peter Zijlstra , Thomas Gleixner , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: x86: missing FRED #PF event data? Message-ID: <20260810110624.06a86a74@pumpkin> In-Reply-To: References: <20260810090347.GS48970@noisy.programming.kicks-ass.net> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) 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=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 10 Aug 2026 18:09:43 +0900 Sergey Senozhatsky wrote: > On (26/08/10 11:03), Peter Zijlstra wrote: > > > > > and got the following while running my tests (and well, we don't crash > > > > > anymore): > > > > > > > > > > [ 254.040223] :: fixed up address to ffff9c4d64af4000 [[fred: 0 cr2: ffff9c4d64af4000]] > > > > > ... > > > > > [ 1821.904563] :: fixed up address to ffff9c4e9dd0a000 [[fred: 0 cr2: ffff9c4e9dd0a000]] > > > > > > > > > > Does any of this make sense to you? > > > > > > > > I think the explanation is some pKVM shenanigans. Sorry for the noise. > > > > > > No, I think we are back at square one. I thought that maybe pKVM > > > was disabling FRED and that was causing issues. But I actually see > > > that both cpu_feature_enabled(X86_FEATURE_FRED) and (cr4 & X86_CR4_FRED) > > > claim FRED is enabled, yet fred #PF data is 0 while CR2 holds the correct > > > address. > > > > Can you reproduce on real hardware? I mean, you were babbling about pKVM > > (whatever that is), so I'm thinking you're on some dodgy virt thing. > > > > Not that I have any actual FRED hardware to test anything on :/ > > It's an actual H/W, a laptop (Intel(R) Core(TM) Ultra 7 355 powered), > I was babbling about pKVM because it seems that the best way to > reproduce is to launch a VM, yet the crash is happening on the host > side. > Is the same fault processed correctly from userspace? If not it might be easier to test. David