From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 057F424B34 for ; Tue, 25 Jun 2024 09:10:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719306605; cv=none; b=cijkN3n/60MbzW2RHZ4O93B1jBT/UM7uk+6YREwgTf/j/LRxkXUbmOGq3b5j4TI2MK2nL99l0owqzYt1Rdc/pisRoEsZbDYwESuPbLfkpgKRcOvf2WQpCU04Q0zCP6hRWa20uK3cCRxwH2iHxw+G+2P5k8RZK1wR2GlWzamJioI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719306605; c=relaxed/simple; bh=PgmweWsgyjunXwL2K/VjA1gLM34Omcb+xcKaqJqZuIA=; h=Message-ID:Date:MIME-Version:From:Subject:To:Cc:References: In-Reply-To:Content-Type; b=mF62EC5euLX7MM8VomUC4hyfqbWs71MRdKZYM6PpUEo7POAxhfo33/fu8DQthwWFMg93jc9MC1AokjVxl2m0OkSMkzxgAt69Ria9WdDuZaL49JPAaWgU6ceX++UBT+sc1MwfHUFy6PUAdI9iOLoGiYwg/9ZTF8IGLYXQbGM3UaU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=dQwTZPOd; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="dQwTZPOd" Received: from [192.168.7.205] ([71.202.166.45]) (authenticated bits=0) by mail.zytor.com (8.17.2/8.17.1) with ESMTPSA id 45P99UfG1551074 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Tue, 25 Jun 2024 02:09:31 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 45P99UfG1551074 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2024061501; t=1719306572; bh=iCQ21Qo+mXw3zg+knnXoD23BPWOHBWTkZu2Jd89OruQ=; h=Date:From:Subject:To:Cc:References:In-Reply-To:From; b=dQwTZPOdqm3H9e4BT0bHkN1GekWXtznPothFfWe7/0qWIwxNpEs9Ybi2LaXLXE/EE 2LWlbxIuwxggxad0+QHQa+E9RITysnCImoE/ueJIogbQTWAF97N+HZrqncKx+eP4T2 Wic2tNRighW9s5eF4Sj9O0WqaEPBbvFi2RjmvBh8rQI/tlxikaPaiv+VK5tFfSc38r SYskrjHYAhLeFIjoE3E3znuuQ7o1UyfksL+UIBAK+aLOHSyEspj7J3PJKZP9IKbIDa z4lze9LueMC2cFh2XCvGwrCcDw4aA3HVCc7j/WJpSwAPwv1ewGcWH9v8g3BwjtFA/o snMCzctWhvSBg== Message-ID: Date: Tue, 25 Jun 2024 02:09:29 -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 From: Xin Li Subject: Re: [PATCH 0/2] x86/fred: Fix two problems during the FRED initialization To: Hou Wenlong Cc: linux-kernel@vger.kernel.org, Lai Jiangshan , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Xin Li , Jacob Pan , Rick Edgecombe , Paolo Bonzini References: <58ec98bf-b66c-4249-8a10-ff254cd405c2@zytor.com> <20240624062143.GA59245@k08j02272.eu95sqa> Content-Language: en-US Autocrypt: addr=xin@zytor.com; keydata= xsDNBGUPz1cBDACS/9yOJGojBFPxFt0OfTWuMl0uSgpwk37uRrFPTTLw4BaxhlFL0bjs6q+0 2OfG34R+a0ZCuj5c9vggUMoOLdDyA7yPVAJU0OX6lqpg6z/kyQg3t4jvajG6aCgwSDx5Kzg5 Rj3AXl8k2wb0jdqRB4RvaOPFiHNGgXCs5Pkux/qr0laeFIpzMKMootGa4kfURgPhRzUaM1vy bsMsL8vpJtGUmitrSqe5dVNBH00whLtPFM7IbzKURPUOkRRiusFAsw0a1ztCgoFczq6VfAVu raTye0L/VXwZd+aGi401V2tLsAHxxckRi9p3mc0jExPc60joK+aZPy6amwSCy5kAJ/AboYtY VmKIGKx1yx8POy6m+1lZ8C0q9b8eJ8kWPAR78PgT37FQWKYS1uAroG2wLdK7FiIEpPhCD+zH wlslo2ETbdKjrLIPNehQCOWrT32k8vFNEMLP5G/mmjfNj5sEf3IOKgMTMVl9AFjsINLHcxEQ 6T8nGbX/n3msP6A36FDfdSEAEQEAAc0WWGluIExpIDx4aW5Aenl0b3IuY29tPsLBDQQTAQgA NxYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89XBQkFo5qAAhsDBAsJCAcFFQgJCgsFFgID AQAACgkQa70OVx2uN1HUpgv/cM2fsFCQodLArMTX5nt9yqAWgA5t1srri6EgS8W3F+3Kitge tYTBKu6j5BXuXaX3vyfCm+zajDJN77JHuYnpcKKr13VcZi1Swv6Jx1u0II8DOmoDYLb1Q2ZW v83W55fOWJ2g72x/UjVJBQ0sVjAngazU3ckc0TeNQlkcpSVGa/qBIHLfZraWtdrNAQT4A1fa sWGuJrChBFhtKbYXbUCu9AoYmmbQnsx2EWoJy3h7OjtfFapJbPZql+no5AJ3Mk9eE5oWyLH+ QWqtOeJM7kKvn/dBudokFSNhDUw06e7EoVPSJyUIMbYtUO7g2+Atu44G/EPP0yV0J4lRO6EA wYRXff7+I1jIWEHpj5EFVYO6SmBg7zF2illHEW31JAPtdDLDHYcZDfS41caEKOQIPsdzQkaQ oW2hchcjcMPAfyhhRzUpVHLPxLCetP8vrVhTvnaZUo0xaVYb3+wjP+D5j/3+hwblu2agPsaE vgVbZ8Fx3TUxUPCAdr/p73DGg57oHjgezsDNBGUPz1gBDAD4Mg7hMFRQqlzotcNSxatlAQNL MadLfUTFz8wUUa21LPLrHBkUwm8RujehJrzcVbPYwPXIO0uyL/F///CogMNx7Iwo6by43KOy g89wVFhyy237EY76j1lVfLzcMYmjBoTH95fJC/lVb5Whxil6KjSN/R/y3jfG1dPXfwAuZ/4N cMoOslWkfZKJeEut5aZTRepKKF54T5r49H9F7OFLyxrC/uI9UDttWqMxcWyCkHh0v1Di8176 jjYRNTrGEfYfGxSp+3jYL3PoNceIMkqM9haXjjGl0W1B4BidK1LVYBNov0rTEzyr0a1riUrp Qk+6z/LHxCM9lFFXnqH7KWeToTOPQebD2B/Ah5CZlft41i8L6LOF/LCuDBuYlu/fI2nuCc8d m4wwtkou1Y/kIwbEsE/6RQwRXUZhzO6llfoN96Fczr/RwvPIK5SVMixqWq4QGFAyK0m/1ap4 bhIRrdCLVQcgU4glo17vqfEaRcTW5SgX+pGs4KIPPBE5J/ABD6pBnUUAEQEAAcLA/AQYAQgA JhYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89ZBQkFo5qAAhsMAAoJEGu9DlcdrjdR4C0L /RcjolEjoZW8VsyxWtXazQPnaRvzZ4vhmGOsCPr2BPtMlSwDzTlri8BBG1/3t/DNK4JLuwEj OAIE3fkkm+UG4Kjud6aNeraDI52DRVCSx6xff3bjmJsJJMb12mWglN6LjdF6K+PE+OTJUh2F dOhslN5C2kgl0dvUuevwMgQF3IljLmi/6APKYJHjkJpu1E6luZec/lRbetHuNFtbh3xgFIJx 2RpgVDP4xB3f8r0I+y6ua+p7fgOjDLyoFjubRGed0Be45JJQEn7A3CSb6Xu7NYobnxfkwAGZ Q81a2XtvNS7Aj6NWVoOQB5KbM4yosO5+Me1V1SkX2jlnn26JPEvbV3KRFcwV5RnDxm4OQTSk PYbAkjBbm+tuJ/Sm+5Yp5T/BnKz21FoCS8uvTiziHj2H7Cuekn6F8EYhegONm+RVg3vikOpn gao85i4HwQTK9/D1wgJIQkdwWXVMZ6q/OALaBp82vQ2U9sjTyFXgDjglgh00VRAHP7u1Rcu4 l75w1xInsg== In-Reply-To: <20240624062143.GA59245@k08j02272.eu95sqa> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/23/2024 11:21 PM, Hou Wenlong wrote: > On Sat, Jun 22, 2024 at 08:31:26AM +0800, Xin Li wrote: >> On 6/21/2024 6:12 AM, Hou Wenlong wrote: >>> One issue is that FRED can be disabled in trap_init(), but >>> sysvec_install() can be called before trap_init(), thus the system >>> interrupt handler is not installed into the IDT if FRED is disabled >>> later. Initially, I attempted to parse the cmdline and decide whether to >>> enable or disable FRED after parse_early_param(). However, I ultimately >>> chose to always install the system handler into the IDT in >>> sysvec_install(), which is simple and should be sufficient. >> >> Which module with a system vector gets initialized before trap_init() is >> called? >> > Sorry, I didn't mention the case here. I see sysvec_install() is used > only in the guest part (KVM, HYPERV) currently. For example, the KVM > guest will register the HYPERVISOR_CALLBACK_VECTOR APF handler in > kvm_guest_init(), which is called before trap_init(). So if only the FRED > handler is registered and FRED is disabled in trap_init() later, then the > IDT handler of the APF handler is missing. This is a bug! Your fix looks good to me. >>> Another problem is that the page fault handler (exc_page_fault()) is >>> installed into the IDT before FRED is enabled. Consequently, if a #PF is >>> triggered in this gap, the handler would receive the wrong CR2 from the >>> stack if FRED feature is present. To address this, I added a page fault >>> entry stub for FRED similar to the debug entry. However, I'm uncertain >>> whether this is enough reason to add a new entry. Perhaps a static key >>> may suffice to indicate whether FRED setup is completed and the handler >>> can use it. >> >> How could a #PF get triggered during that gap? >> >> Initialization time funnies are really unpleasant. >> > I'm not sure if there will be a #PF during that gap; I just received the > wrong fault address when I made a mistake in that gap and a #PF > occurred. Before idt_setup_early_pf(), the registered page fault handler > is do_early_exception(), which uses native_read_cr2(). However, after > that, the page fault handler had been changed to exc_page_fault(), so if > something bad happened and an unexpected #PF occurred, the fault address > in the error output will be wrong, although the CR2 in __show_regs() is > correct. I'm not sure if this matters or not since the kernel will panic > at that time. So this doesn't sound a real problem, right? We could simply do: diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index e6c469b323cc..e500777ed2b4 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1495,7 +1495,7 @@ DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault) irqentry_state_t state; unsigned long address; - address = cpu_feature_enabled(X86_FEATURE_FRED) ? fred_event_data(regs) : read_cr2(); + address = native_read_cr4() & X86_CR4_FRED ? fred_event_data(regs) : read_cr2(); prefetchw(¤t->mm->mmap_lock); But the page fault handler is an extreme hot path, it's not worth it. Thanks! Xin