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X-CSE-ConnectionGUID: GG8iPdpZQ12UInbDoorDdw== X-CSE-MsgGUID: D2UCg9JTRsy9R4/5SlBYzQ== X-IronPort-AV: E=McAfee;i="6700,10204,11351"; a="44813768" X-IronPort-AV: E=Sophos;i="6.13,302,1732608000"; d="scan'208";a="44813768" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by fmvoesa106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Feb 2025 15:00:43 -0800 X-CSE-ConnectionGUID: 555xKCyBQcaqzopAHLdo/A== X-CSE-MsgGUID: 53EqsSUlSrqMna1u14ATsg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.13,302,1732608000"; d="scan'208";a="138402913" Received: from jdoman-mobl3.amr.corp.intel.com (HELO [10.125.110.142]) ([10.125.110.142]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Feb 2025 15:00:42 -0800 Message-ID: <9053a4ef-2de6-47b4-a2f7-62d3ded24cfa@intel.com> Date: Thu, 20 Feb 2025 15:00:43 -0800 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V5 2/4] x86/tdx: Route safe halt execution via tdx_safe_halt() To: Vishal Annapurve , x86@kernel.org, linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, virtualization@lists.linux.dev Cc: pbonzini@redhat.com, seanjc@google.com, erdemaktas@google.com, ackerleytng@google.com, jxgao@google.com, sagis@google.com, oupton@google.com, pgonda@google.com, kirill@shutemov.name, dave.hansen@linux.intel.com, chao.p.peng@linux.intel.com, isaku.yamahata@gmail.com, sathyanarayanan.kuppuswamy@linux.intel.com, jgross@suse.com, ajay.kaher@broadcom.com, alexey.amakhalov@broadcom.com, stable@vger.kernel.org References: <20250220211628.1832258-1-vannapurve@google.com> <20250220211628.1832258-3-vannapurve@google.com> 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 2/20/25 13:16, Vishal Annapurve wrote: > Direct HLT instruction execution causes #VEs for TDX VMs which is routed > to hypervisor via TDCALL. safe_halt() routines execute HLT in STI-shadow > so IRQs need to remain disabled until the TDCALL to ensure that pending > IRQs are correctly treated as wake events. This isn't quite true. There's only one paravirt safe_halt() and it doesn't do HLT or STI. I think it's more true to say that "safe" halts are entered with IRQs disabled. They logically do the halt operation and then enable interrupts before returning. > So "sti;hlt" sequence needs to be replaced for TDX VMs with "TDCALL; > *_irq_enable()" to keep interrupts disabled during TDCALL execution. But this isn't new. TDX already tried to avoid "sti;hlt". It just screwed up the implementation. > Commit bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests") > prevented the idle routines from using "sti;hlt". But it missed the > paravirt routine which can be reached like this as an example: > acpi_safe_halt() => > raw_safe_halt() => > arch_safe_halt() => > irq.safe_halt() => > pv_native_safe_halt() This, on the other hand, *is* important. > Modify tdx_safe_halt() to implement the sequence "TDCALL; > raw_local_irq_enable()" and invoke tdx_halt() from idle routine which just > executes TDCALL without toggling interrupt state. Introduce dependency > on CONFIG_PARAVIRT and override paravirt halt()/safe_halt() routines for > TDX VMs. This changelog glosses over one of the key points: Why *MUST* TDX use paravirt? It further confuses the reasoning by alluding to the idea that "Direct HLT instruction execution ... is routed to hypervisor via TDCALL". It gives background and a solution, but it's not obvious what the problem is or how the solution _fixes_ the problem. What must TDX now depend on PARAVIRT? Why not just route the HLT to a TDXCALL via the #VE code?