From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.216.72 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793822338; b=KbKXcdpCdVog0zpxFgmI6zQhxcWzbLHkmk2ci8+fLI4i+ykfIMLZvIDHedBGFj0E03qe S+AAnmIFeE1YBh5p4DfZyGJ5q38ncYba+6e/TTNr/jsiBDWoyGrN9HMNn6UO7VKpdutyg pJ7Zkd0oqTTMJ39qUpZxbp/OrIXTSaSrw9IiEnq/hFuwqYnXt1UheVAvTKxbjrNaGmHet nDUUCYVsG54K64Sl7bGdajarzoMvd/XM8SOPq3cKqEhEdlTUGWYB7wgbzLHczzHEaIGNr o+PkvmdY1pjTnYDK2pRT/V5Lqlyu429k/0yI/DP8OIeiAp3KfcQHRkI7tpcIDhOEwmA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793822338; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Received:Date:In-Reply-To: Mime-Version:References:Message-ID:Subject:From:To:Cc:Content-Type; bh=EHk5yeUEIXC7UFrXwF/Qx/XTGMvkxGfWmAK/i22vALA=; b=JKAJABk5CVu8b1o4EKThWeIr33Fer5i6ThZpjOKqtiztx5lFOv+UW/B6O3M8kNt2/c1k R0cKwOG4zY+l9PZr7GlpULGM/bDWrUIDCtnxZqLDbYBhVkV2WZo3+N9367HColXwbvpYN SRSUqjawDT5cwse21X/cQ5R7PYfyTaCGW8AInOzITUgw3TnSSWZgHMfcgrauOyxIvRaik jre7YY/3qgOKMNmmgJlWxEOLwiyvPh5dgFdWwtEAJYHWlqpfHngT+eTtHvXzIO98ijiTn CoeKHodZpZeAh5LxjsLAjhn3r7LlSu2IAfS1aM6bdHZ1IYDIeHdzyUk8cdT6pdU/knQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20260707 header.b=P388IfTt; arc=none smtp.remote-ip=209.85.216.72 Received: from mail-pj1-f72.google.com (mail-pj1-f72.google.com [209.85.216.72]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 220C2606D4D9 for ; Wed, 4 Nov 2026 19:58:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 220C2606D4D9 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, unprotected) header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20260707 header.b=P388IfTt Received: by mail-pj1-f72.google.com with SMTP id 98e67ed59e1d1-3adc5b185bfso1226596a91.3 for ; Wed, 04 Nov 2026 11:58:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20260707; t=1793822337; x=1794427137; 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=EHk5yeUEIXC7UFrXwF/Qx/XTGMvkxGfWmAK/i22vALA=; b=P388IfTtlWm2shzuTrtWSPHnZifKhxpoiP7raetv2aDxaF7+9d6u7xEpTB5u7KEe/F fwFKjk7docwBVEMjxr63/85Asdm4EBZ1VNn+3e/Oxl6BityVcLbHDYuJXqf+xbklfuIA /VLyXTs/lMSSTCo4q8jig8etOM8OmGRhe8mAaJgz75CN+wL5XmM8BtQkdMdnqFY1QLhB cIDJpOxlpEvFPqynH01/IBQZEAFEDErzC8+jCKj9pfBzaNuynqe1VmjoCihrt2DcqPPa XFsM2d7gIaA8H4E3DMcq+1x6RgzSi6t540TuBV5bzvn0fJoOEk+3gCbGdt/v6ezH2LTn 7wmQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1793822337; x=1794427137; 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=EHk5yeUEIXC7UFrXwF/Qx/XTGMvkxGfWmAK/i22vALA=; b=W9nHDz4xCEiqJ3gEQ1tdmZ1wbdB5FGE3bJ16SQLaKrTjV+lEaQBEm+4cyxEADbjByr fXZ1rLVaFZmTHVfe1wVugpluikBDEU3NcoYJ6e/8CAQib/akJv622WCCyRud5VidYYNT VfRG0IhGExblrevzAV3yJR5Lz3W6rdgh6tZoHRf2F1jgJwW1EU16Nc5YE0sX+dV6tuAP h7vSy+eLFL+jBevpbAMC7SfLDU0nRWM8eqg9Uj7MLVxEos0124ImJ5upbILzgumz2e2I TgDX33W1s+R7CnD7aoyzjZx8TYSuUmFbGfJbmAC2LEFyCksdnosvMmVe1HG1RfjhPpwj EeDQ== X-Forwarded-Encrypted: i=1; AKwUvBzhB71EKPAxbmf+ieMeJetFRKuM9X35hTlrOzZn0iBJRFHgJ693TpZcKJkt8uV3Y58eP2o=@vger.kernel.org X-Gm-Message-State: APuU4Z9FeF9/xPiTgREl4LbKh9a6eFTFTOK4agUdDBwM/hDYA/Jatbmm 7F6wRBLBSDAzOl8nmk4YCBVYjnwpcjA5PUqyJyd7WbrKbA26P1fdVldme2GqYzmdZvaCyKAkdcx L9xLgCw== X-Received: from pjwt8.prod.google.com ([2002:a17:90a:d148:b0:3ac:c43b:e307]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90a:d803:b0:3b0:9a0d:b825 with SMTP id 98e67ed59e1d1-3b09a0db95fmr1809747a91.45.1793822337303; Wed, 04 Nov 2026 11:58:57 -0800 (PST) Date: Wed, 4 Nov 2026 11:58:56 -0800 In-Reply-To: X-Mailing-List: kvm@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 References: Message-ID: Subject: Re: [PATCH] KVM: x86: Emulate SYSENTER in 64-bit mode for Intel-compatible vCPUs From: Sean Christopherson To: Hao Zhang Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Wed, Oct 21, 2026, Hao Zhang wrote: > From: Hao Zhang > > Intel allows SYSENTER in both IA-32e submodes, whereas AMD raises #UD > in either submode. On AMD hosts, KVM intercepts #UD and emulates > SYSENTER to support Intel-compatible vCPUs. > > However, em_sysenter() unconditionally rejects execution from 64-bit > mode. As a result, a valid SYSENTER in an Intel-compatible guest can > fail emulation instead of entering the guest's kernel. For a > non-nested guest at CPL0, this results in a > KVM_INTERNAL_ERROR_EMULATION exit to userspace even when > KVM_CAP_EXIT_ON_EMULATION_FAILURE is not enabled. > > Remove the unconditional rejection. Why? I'm not inclined to expand the emulator's capabilities for something like this without a *really* good reason to do so.