From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1572E225D7 for ; Fri, 12 Apr 2024 22:46:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712961970; cv=none; b=KFvMAlwwJjKyG6U32ZX+mPBkaYLmIQdNDPkdo+RtNYPDWnjYw025ZvpmvvW58RMFXW4nvjA8Pgs2/AWY0xn05ToKb56TNTXwju9L8RMPpW5iwJdv4F4SlgmsylTfUmS93OyATA/nC09B8E959SIpTmyrGIumgRwLHqrcpPMahU8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712961970; c=relaxed/simple; bh=CVh3GoQ0Uj5EBqBGfQw29CTm8/4AiBhdQKue4WhQnYU=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=uA+yer486yedxFmA98ewFOvr57uMH0IAOYK81/yD4hVF5wS7KrMyY/BNBXCjd1hhjE5QSSGo8ijwRdhfV8a9U3LjyDSp32//Bi05IEclXj9pe/G59ld7hraVvlN3Xab2il+dXT1BIzvlrCp4wAG+SpCY1GJySmj15hCOFrJUQcU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=gfb0AnLA; arc=none smtp.client-ip=209.85.216.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="gfb0AnLA" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-2a4f128896aso1863217a91.1 for ; Fri, 12 Apr 2024 15:46:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1712961968; x=1713566768; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=azAaAXQ+5slCG5tLzAxZ1/q0F1Xu5c3tqFk5gSJfnGk=; b=gfb0AnLAz5bQDguarqegI62fEl7QhQxdhTLJvbWhhi7FN6MfeZSqs05/8EcIQmHUf1 /IfV749FMMl8LiA0JGJM2km8cTl/NCuIyy/dw2EHsXT0oVWlPEbB8zUPBDn6H2DTxUOY xCCjJaGyUELxscJ5eLaXyTaB+7rQjCiRaQ+OzeAmbqOE6hQhGOF0IipR9hLB2vizyDU4 ZKr5uVuOxcQR/3/yONHemnM40qwh2C0tmmvQ5xgwb/Pti89TXhZtZk4z/t0KqI8Y7+wh 82ExeSqQO1G6VO2HVdENfgcNeXIMSGvKdI6qAez06CeiPj9MmnUOUEHQZKRH2H8L8aUC O37g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1712961968; x=1713566768; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=azAaAXQ+5slCG5tLzAxZ1/q0F1Xu5c3tqFk5gSJfnGk=; b=mp2006SH9iOB3ktr+SFocXdiawmy0An67GCEosEGO3BLK8jBET9GkN4jf08ubRVcl9 ILWUjVnCOBPX9ybpA09lMIkZv479+8DrBngpM9afqvXT5dh04nMZ3CU0GPmepcrVKxrR OYH48BBsgfaK5D8DWmSvxMkxjLR/2uW1FWdcBNAYUifNY1R9UYR7cd6U+e+unNLN6RI1 e7XlKT4P37TFUd+MYezABRhRLEb5pWd8Syvg/Y4EySGwbTkbegt+oSYkGRXW0yrZZmOD ncB6nADwdSk0dtdxoChIz6ICtekaqxWLd/CjkDlDlP+GeqAbgo98KRsU/07NGfb7RKpq mWww== X-Forwarded-Encrypted: i=1; AJvYcCXg0xr3jYPR4t8mMnlKqu4o0QdgxykRF1QEaqK8s67OpCHcRQT4+mowJlmbXnWSSgCpHpZzzd4yZsVOaJXcK7LFEZjk X-Gm-Message-State: AOJu0YwKxSvDskLB6nDkuPNcAr/9hBcjrtS/mt4j7VrJNiL80IANSh99 JnBuc51DqjAp074ISTQjLcqPcTSVM3b7gqvsOd2+tPs7yydImFUM/3l6a5AhLzBoUwWdKCmzgbJ BTg== X-Google-Smtp-Source: AGHT+IEa78IMUBOreaXnhO8WKAdssc3iFz0oqiOvqMH5Yz6szB/OqGs806267bfnDoRjxI6Hb7/ZXyDX410= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a17:90a:a392:b0:2a6:f288:53da with SMTP id x18-20020a17090aa39200b002a6f28853damr12661pjp.3.1712961967328; Fri, 12 Apr 2024 15:46:07 -0700 (PDT) Date: Fri, 12 Apr 2024 15:46:05 -0700 In-Reply-To: <20240412214201.GO3039520@ls.amr.corp.intel.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <0c3efffa-8dd5-4231-8e90-e0241f058a20@intel.com> <20240412214201.GO3039520@ls.amr.corp.intel.com> Message-ID: Subject: Re: [PATCH v19 087/130] KVM: TDX: handle vcpu migration over logical processor From: Sean Christopherson To: Isaku Yamahata Cc: Reinette Chatre , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, isaku.yamahata@gmail.com, Paolo Bonzini , erdemaktas@google.com, Sagi Shahar , Kai Huang , chen.bo@intel.com, hang.yuan@intel.com, tina.zhang@intel.com, isaku.yamahata@linux.intel.com Content-Type: text/plain; charset="us-ascii" On Fri, Apr 12, 2024, Isaku Yamahata wrote: > On Fri, Apr 12, 2024 at 09:15:29AM -0700, Reinette Chatre wrote: > > > +void tdx_mmu_release_hkid(struct kvm *kvm) > > > +{ > > > + while (__tdx_mmu_release_hkid(kvm) == -EBUSY) > > > + ; > > > } > > > > As I understand, __tdx_mmu_release_hkid() returns -EBUSY > > after TDH.VP.FLUSH has been sent for every vCPU followed by > > TDH.MNG.VPFLUSHDONE, which returns TDX_FLUSHVP_NOT_DONE. > > > > Considering earlier comment that a retry of TDH.VP.FLUSH is not > > needed, why is this while() loop here that sends the > > TDH.VP.FLUSH again to all vCPUs instead of just a loop within > > __tdx_mmu_release_hkid() to _just_ resend TDH.MNG.VPFLUSHDONE? > > > > Could it be possible for a vCPU to appear during this time, thus > > be missed in one TDH.VP.FLUSH cycle, to require a new cycle of > > TDH.VP.FLUSH? > > Yes. There is a race between closing KVM vCPU fd and MMU notifier release hook. > When KVM vCPU fd is closed, vCPU context can be loaded again. But why is _loading_ a vCPU context problematic? If I'm reading the TDX module code correctly, TDX_FLUSHVP_NOT_DONE is returned when a vCPU is "associated" with a pCPU, and association only happens during TDH.VP_ENTER, TDH.MNG.RD, and TDH.MNG.WR, none of which I see in tdx_vcpu_load(). Assuming there is something problematic lurking under vcpu_load(), I would love, love, LOVE an excuse to not do vcpu_{load,put}() in kvm_unload_vcpu_mmu(), i.e. get rid of that thing entirely. I have definitely looked into kvm_unload_vcpu_mmu() on more than one occassion, but I can't remember off the top of my head why I have never yanked out the vcpu_{load,put}(). Maybe I was just scared of breaking something and didn't have a good reason to risk breakage? > The MMU notifier release hook eventually calls tdx_mmu_release_hkid(). Other > kernel thread (concretely, vhost krenel thread) can get reference count to > mmu and put it by timer, the MMU notifier release hook can be triggered > during closing vCPU fd. > > The possible alternative is to make the vCPU closing path complicated not to > load vCPU context instead f sending IPI on every retry.