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X-CSE-ConnectionGUID: GXvnw0QkS/a1tlZxjnIz3g== X-CSE-MsgGUID: fytc5eYHT6+IV+F8zpHNZw== X-IronPort-AV: E=McAfee;i="6600,9927,11093"; a="14207007" X-IronPort-AV: E=Sophos;i="6.08,214,1712646000"; d="scan'208";a="14207007" Received: from fmviesa010.fm.intel.com ([10.60.135.150]) by orvoesa108.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Jun 2024 09:01:01 -0700 X-CSE-ConnectionGUID: nye2neQtRJSZaJn3uapRtA== X-CSE-MsgGUID: 5W+Z/73WSKuecZp17OX15Q== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.08,214,1712646000"; d="scan'208";a="37362374" Received: from cdpresto-mobl2.amr.corp.intel.com.amr.corp.intel.com (HELO [10.125.108.218]) ([10.125.108.218]) by fmviesa010-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Jun 2024 09:01:00 -0700 Message-ID: <3f15814c-de9c-4aa6-b56d-82761bb6520a@intel.com> Date: Tue, 4 Jun 2024 09:00:59 -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: [PATCH 1/4] x86/entry: Remove unwanted instrumentation in common_interrupt() To: Dmitry Vyukov , tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org Cc: linux-kernel@vger.kernel.org, syzkaller@googlegroups.com, elver@google.com, glider@google.com, nogikh@google.com, tarasmadan@google.com, Peter Zijlstra References: <1ada3be307bbd076c4ea63530cf445e7fbd0e4e7.1717507310.git.dvyukov@google.com> Content-Language: en-US From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/4/24 06:45, Dmitry Vyukov wrote: > The manifestation is that KCOV produces spurious coverage > in kvm_set_cpu_l1tf_flush_l1d() in random places because > the call happens when preempt count is not yet updated > to say that we are in an interrupt. > > Mark kvm_set_cpu_l1tf_flush_l1d() as __always_inline and move > out of instrumentation_begin/end() section. > It only calls __this_cpu_write() which is already safe to call > in noinstr contexts. I've internalized the main rules around noinstr to basically be: Only call noinstr functions before begin_instrumentation(). Second, try to minimize the amount of noinstr code. This patch seems to be adding another rule which is that all code before preempt_count manipulation needs to be noinstr. _Is_ that a new rule, or was it something I was missing?