From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f197.google.com (mail-pl1-f197.google.com [209.85.214.197]) (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 399A544470E for ; Mon, 17 Aug 2026 18:19:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.197 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786990759; cv=none; b=uQL2cl9Ud3J5WjTfBaDVnn7ji8sTexlHq6tluYqYU3e6rYAOrEXmPp3AxyOgXb3Euxxifn7E8jSY1Zx20F3nS9cfU+l29722zYmGN7zZbx1kBBut0iT+75a0RyYxl5TOnwfea+PrdFprB00PIrpxDIf4wkREx79iYlNoo00FFGg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786990759; c=relaxed/simple; bh=61l/vR22wAGj+G5ncDTVr+gQ+Yzx1sQDDhvKkefO+PM=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Vsaj6oIXjqSQFoh/Is2Bqo1P6O/M2Q0uCLw9RPZIK8VgZE2guOYUdzv3xpXCX8CYKD83WzG+zCidYjQgOPg+PPGYRunVzoxZEPIXNLAO6UYImGFrjRUPzkc4yamMk/Q/CR5OL1pcAZ/utO2ARrWSTS7lx+fu/Zl//R+s4zygwIM= 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=PAX8+OuF; arc=none smtp.client-ip=209.85.214.197 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="PAX8+OuF" Received: by mail-pl1-f197.google.com with SMTP id d9443c01a7336-2cccfa32670so51773125ad.2 for ; Mon, 17 Aug 2026 11:19:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1786990757; x=1787595557; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=BhiYLD9VDgA0P+vwZ8hZo0EEnFAN1wOjxc6IU0ZbmYw=; b=PAX8+OuFoyDJ3I7uwxmk9sEB6/WzTw6owNaqNvD51Da5+3YzpR/KVLeP7xiC8sd80/ FH0ypm8ZGOxOMElGLvWbJbMF7v1EXmFaFnG3VOlikdLiGo18mxlf1EH4QeYDU0JOkUVV JjPEC8pJS8r+RsTdBwm3KZiOxiF5ycmha8JFBU6SS2hPVqWpvZAJfHoBU47NKL9aOoCW 6Q4X6YbVFcrg9W9GNA9WPNPVfT33QRmqxJRhBd17oPjBWs79nNz6humL3so8qqAfHp7I TdIIWIEADh8bgyd5yapVSg2IydEMnse40oJKjcMGcjUDkXcDDkhpMO5FeRuBGtjOe/bW P/6A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786990757; x=1787595557; h=content-type: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:content-type; bh=BhiYLD9VDgA0P+vwZ8hZo0EEnFAN1wOjxc6IU0ZbmYw=; b=NWig2SAuKM+mIMLXFkt8nFF4bcA2+rKdSaKVyTkZXxGVqLanoKQBk9+7V0toDAqf5y 8JuUDB1Mbe+Cdz7E7vlf1GEjJrrKWlIy5AThntC6VQOvu1v7p0Tic17qz/hjKrs/srYP CcF6Hnv0fBiyyWWDRPhvbU+tKMpHvjKaPDtqroqr2vFOtlt3c3RGIbKv0/mWCbQzAiql bHQbtsDjiuQDoWOGDN8ZJK4qEuEp0FfSJoksXXTf6CSm/+bXB481wnGF70X2z7XMm5sY vKDRzCiT0QZSILLx66BW13aEsGRLiaSVlC7ySkLQiqfVnxQqmtgaRhGiugsWhBMjjYBT M/6A== X-Forwarded-Encrypted: i=1; AHgh+Rowh5VgqvR8V4a5CTq4rlBHjpCml6qRoyBztXcrtaYEJkPSc6ilqvgXLK8trV1LDjKV1fM=@vger.kernel.org X-Gm-Message-State: AOJu0YwU2ySIQsMt/1RlQZuA+tp0CNbj0sHsDHzadVUS5541zZeD7sW7 obsEjxdtYOMgIMbob+AeBwGsoBodYjAqR4gjdrrDYvYf6Dhr5LR9dzuXRKo27RDv6ROaeT/Gtom eJO0vsQ== X-Received: from plbmm15.prod.google.com ([2002:a17:903:a0f:b0:2d1:4ca3:d32b]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:1ab0:b0:2c0:a555:80d6 with SMTP id d9443c01a7336-2d3b0d780e9mr288678215ad.2.1786990757388; Mon, 17 Aug 2026 11:19:17 -0700 (PDT) Date: Mon, 17 Aug 2026 11:19:16 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260812080229.2481439-1-xiaoyao.li@intel.com> <20260812080229.2481439-4-xiaoyao.li@intel.com> <20260812082306.11E8B1F000E9@smtp.kernel.org> <8b05ead1-ef2c-472f-a613-bcd1a65b64e1@intel.com> <138969948dac13369ddebd72bf523dda4dda6b85.camel@intel.com> Message-ID: Subject: Re: [PATCH v3 3/4] KVM: TDX: Don't assume exit_reason[31:16] as all-0 in tdx_to_vmx_exit_reason() From: Sean Christopherson To: Xiaoyao Li Cc: Rick P Edgecombe , "sashiko-reviews@lists.linux.dev" , "pbonzini@redhat.com" , "kvm@vger.kernel.org" Content-Type: text/plain; charset="us-ascii" On Mon, Aug 17, 2026, Xiaoyao Li wrote: > On 8/14/2026 11:12 PM, Sean Christopherson wrote: > > On Fri, Aug 14, 2026, Xiaoyao Li wrote: > > > On 8/14/2026 7:44 AM, Sean Christopherson wrote: > > > > On Wed, Aug 12, 2026, Rick P Edgecombe wrote: > > > > > Side note. I really dislike how tangled this area is for something that seems > > > > > like it should be much more straightforward. Deriving partially I think from the > > > > > overloading of the TDVMCALL leafs with the exit reasons. So we have things like: > > > > > ... > > > > > case EXIT_REASON_EPT_VIOLATION: > > > > > return EXIT_REASON_EPT_MISCONFIG; > > > > > ... > > > > > > > > I peeked at that code again, and FWIW I still think swizzling the exit_reason for > > > > TDVMCALL is the least awful solution. If we don't do that, then we'll have to > > > > update every single use of the exit_reason to demux TDVMCALL into the "real" exit > > > > reason, which will be a mess. > > > > > > I'm not sure if you read my idea[1]? > > > > > > I think there is only one place KVM cares about the exit_reason TDVMCALL, > > > just the > > > > > > case EXIT_REASON_TDCALL: > > > > No, the massaged exit_reason is also subtley consumed via trace_kvm_exit(). > > yeah. This is exactly the one I don't like, it looks like trace_kvm_exit() > is tracing the wrong exit reason, though it is by intentional. > > > It's also consumed by tdx_complete_emulated_msr(): > > > > if (vmx_get_exit_reason(vcpu).basic == EXIT_REASON_MSR_READ) > > > > and by tdx_interrupt_allowed() > > > > return vmx_get_exit_reason(vcpu).basic != EXIT_REASON_HLT || > > !to_tdx(vcpu)->vp_enter_args.r12; > > > > and by tdx_protected_apic_has_interrupt(): > > > > if (vmx_get_exit_reason(vcpu).basic != EXIT_REASON_HLT || > > to_tdx(vcpu)->vp_enter_args.r12) > > return false; > > Ah, I really should have checked the code more carefully. > > > > in tdx_handle_exit(). > > > [1] > > > https://lore.kernel.org/all/646f9595-459f-4224-b4e5-4ec2eecc0bc6@intel.com/ > > > > And once we track the exit_reason separately from vp_enter_ret, IMO it all becomes > > > > more logical and easier to follow. vp_enter_ret holds the information about why > > > > VP.ENTER returned/exited, while exit_reason holds information about why the _guest_ > > > > exited. Obviously it's imperfect since we're still fudging EXIT_REASON_EPT_MISCONFIG, > > > > but again, I think that's a better alternative than demuxing exit_reason in multiple > > > > locations. > > > > > > The question do we really need to swizzle EXIT_REASON_TDCALL to other exit > > > reasons ahead? why cannot them just be handled in the central handler for > > > EXIT_REASON_TDCALL? > > > > Because as above, it's not as central as you think. If we want to not swizzle > > the exit_reason, then IMO the only sane way to do that is to not track exit_reason > > for TDX vCPUs, i.e. move vcpu_vt.exit_reason back to vcpu_vmx and force TDX to > > always demux vp_enter_ret every time. > > How about adding a specific field to track the TDVMCALL leaf? Full diff as > below (the EPT MISCONFIG part can be split into a separate one) I like it even less than demuxing vp_enter_ret on demand. It has all the same flaws as demuxing vp_enter_ret, because it's effectively just a cache of the result of demuxing vp_enter_ret. And caching values on entry/exit boundaries adds additional risk; I can point you at a number of bugs in the past where KVM consumed stale data, e.g. because some chunk of code got moved to run before a cached field was refreshed. That's unlikekly to be a problem here, but anytime data is cached it introduces risk of consuming stale data. And the cost of demuxing vp_enter_ret every time doesn't concern me, at all. What I don't like is relying on call sites to know that the exit_reason needs to be demuxed in the first place, because that will be brittle and error prone. That's why I'd be ok if vcpu_vt.exit_reason simply didn't exist: it becomes impossible to check the wrong exit field because there's only one such field. I'm ok caching the fully processed vcpu_vt.exit_reason, i.e. with the code now, because only the TDVMCALL path needs to be aware that it may have undergone processing, *and* KVM can WARN if that processing didn't happen as expected. Whereas checking the "right" exit reason requires doing so in multiple paths and doesn't have a natural sanity check.