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X-CSE-ConnectionGUID: gbtx83M1SdOc2DICiu4OAg== X-CSE-MsgGUID: E9qcZpMWSZm9zqLEMOBWUw== X-IronPort-AV: E=McAfee;i="6800,10657,11898"; a="111912884" X-IronPort-AV: E=Sophos;i="6.25,265,1779174000"; d="scan'208";a="111912884" Received: from orviesa008.jf.intel.com ([10.64.159.148]) by orvoesa101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Sep 2026 12:12:56 -0700 X-CSE-ConnectionGUID: cQyrjwFrTQGOkpYRj2GVaQ== X-CSE-MsgGUID: oMRqnj9XTdmrG3bhpI3Y2A== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,265,1779174000"; d="scan'208";a="270012387" Received: from smithj1-mobl2.amr.corp.intel.com (HELO [10.125.111.58]) ([10.125.111.58]) by orviesa008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Sep 2026 12:12:55 -0700 Message-ID: <1987b7d6-7aa3-4bcd-9082-f2cdfde7c1e4@intel.com> Date: Sun, 6 Sep 2026 12:12:54 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [tip: x86/urgent] x86/mm/pat: Fix effective RW computation in lookup_address_in_pgd_attr() To: Nathan Chancellor Cc: Mike Rapoport , Dave Hansen , linux-tip-commits@vger.kernel.org, Juergen Gross , "Lorenzo Stoakes (ARM)" , syzbot@syzkaller.appspotmail.com, Atish Patra , Nikunj A Dadhania , stable@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra References: <20260813-cpa-fixes-v2-5-39b4ff90f91d@kernel.org> <178837401172.3717435.314324339347590321.tip-bot2@tip-bot2> <20260905044253.GA3816371@ax162> <20260906181247.GA1148584@ax162> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/6/26 11:12, Nathan Chancellor wrote: > On Sun, Sep 06, 2026 at 07:50:26AM -0700, Dave Hansen wrote: >> On 9/4/26 21:42, Nathan Chancellor wrote: >>> I just bisected the following warning on a couple of my test machines to >>> commit 453e78594434 ("x86/mm/pat: Fix effective RW computation in >>> lookup_address_in_pgd_attr()") in next-20260904. >> ... >>> If there is any information I can provide to help debug this, I am happy >>> to provide it. >> >> Well, the thing you bisected to is the patch that fixes the warning. The > > Hmmm, I don't see a warning prior to this patch though. Do you mean that > this patch is just revealing the bad behavior that you mention below? Yeah, "fixes" was a bad word to use. The W^X detection has been broken for a while. The patch you bisected to fixes the W^X detection. It doesn't actually cause the issue. >> actual issue comes from: >> >> if (pages == &its_pages) >> set_memory_x((unsigned long)page, 1); >> >> which its_alloc() does on an execmem allocation. Any chance you could >> get the output of: >> >> /sys/kernel/debug/page_tables/current_kernel >> >> for the page that page that it's complaining about? I'm curious if this >> is temporary or permanent. > > Sure. For > > CPA detected W^X violation: 8000000000000123 -> 0000000000000123 range: 0xffffffffc0200000 - 0xffffffffc0200fff PFN 100e00 > > I think it is this line if I understand correctly? > > 0xffffffffc0200000-0xffffffffc0400000 2M ro PSE GLB x pmd Yeah, that does seems to show it getting fixed up. Thanks! That means that the warning (at least in early boot) is essentially a false positive. The problem is that there's module-load-time patching too and that is much later and is arguably an actual problem. Oh, and thinking about it a bit more... This warning came from alternatives patching which is too early for normal text_poke(), thus the existence of text_poke_early(). Anyway, I'm curious what Peter wants to do with this.