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 4C433346AC6 for ; Wed, 14 Jan 2026 19:42:47 +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=1768419768; cv=none; b=oKgUOYUA08qqHlrJTuB2n6vbx4/8ethsPsxG93IosKBy1bB9CMryHbN9f1BlbL1RKgpj9KUhDvWffnu3s6k6WswPXu/VPRPe0K9nGf5+xKVT1byRWcZXADbK/Ly+w+fB4ZSrTIlZxPZfKV/00AyBvcrKAtfjL57go3xut3encTg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768419768; c=relaxed/simple; bh=tJLM3EVPIjwolJnxGvjBiFwtKxPitpUwshSr1wSuMyo=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=ISHC1t06zGO7CmqxxukGINDhKNKZyJbdkGA9kid2LWZFcoMdpwd4+4FYBDULLvqUHPSJrS+gcQGidYcvmtqPXSbG/387SvOjRKwtXjoklr+hj9L9atYfWHkPyFAfzO81jxBc9Dqqm0SEnlDlDat3/T68PHk189aiVS98NFxhjqQ= 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=t6aTq1O3; 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="t6aTq1O3" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-34aa6655510so79340a91.1 for ; Wed, 14 Jan 2026 11:42:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1768419767; x=1769024567; 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=9qi7dt3Dd/aVuAS5ol/gIpMZCnZnmJVwzmEj9I8BYxY=; b=t6aTq1O3lawodb3Y9hM79sXGSqUZk/3obql0wTVJXaxGVBJaBsvD3FK3Abc7SQyhbd gXjMAR9pwN8ZmF7/PJ85kRsaeTVNAjNjuuRZ3ZZxB6QeZYIps4ue/GHQhea0Hw+voiH/ Z0X3qtCKcCZo+7e/H6A0ttvG/iyEoMGjXOkAPldg4XFPap/8dDHzgR+kNVPGFnKlJA5O I9sgVNHHwOczkTSPzTYGZu/sm186TsEP4u/8p+9OCcuHPAOSneVe8cy3OBLVW0XatXV6 45K3xtYIyrogGATQaZ5iU6nOmSwIBWyilJ5/aKjgMEtyV2UAqRoPAdYClUZaVgR7WcyB 3+Gw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1768419767; x=1769024567; 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=9qi7dt3Dd/aVuAS5ol/gIpMZCnZnmJVwzmEj9I8BYxY=; b=ZLeSV5EOYDRU7nUq01E++QvA26GtI9WNAg+twjbcUjMZEvdgleRs/keAaNWphqYlS4 iVL1AlTCb6VEjViNPPbL8TGZ0kGm4Y32CZd/xROmg5y9nJZUi141pjE5M+f/2ZKCvMPX iOZGK46PuLS8Ko3hu1y82WX979YpyWRo29Icy8OOtzdb3U19XDCME6uq5GpAGkgiw8Cx fwcKgqS5tuw6wyh+uA5AXpYIzYMVe6Oryomt40JkdkI7VG6N9GjB0+9pBzGc7+J4IvHs pWFd6zEAArorJ2m+pKPBkiDN+O2zCb1yM/6R20Jce+ZOjge0n8wNruLtfgNsjJt5uDsy LyiQ== X-Forwarded-Encrypted: i=1; AJvYcCXrByiSmitc3qQU6D2Ghp/8FSSWF4R9EnlsDHNgXZuyNHk1FGhvDMVGmDz1P6sC2ujkHZM=@vger.kernel.org X-Gm-Message-State: AOJu0YxlAjbPsHKUPGEjl0WLcGszoYtKtY+mEBu2gk6o3HO+N+F8kQSS KOwh+iXqqXy6xDIqe/LqaZxgxmLt+WHJvql/xQEbKdCjsS2fwqXcyv1Ak55Cqki4aTdBH3aJo8F LvKBw1Q== X-Received: from pjbkb14.prod.google.com ([2002:a17:90a:e7ce:b0:34c:cc12:1613]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90a:e7c1:b0:343:d70e:bef0 with SMTP id 98e67ed59e1d1-3510911fba8mr3604743a91.21.1768419766622; Wed, 14 Jan 2026 11:42:46 -0800 (PST) Date: Wed, 14 Jan 2026 11:42:44 -0800 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260112232805.1512361-1-seanjc@google.com> Message-ID: Subject: Re: [PATCH] KVM: SVM: Check vCPU ID against max x2AVIC ID if and only if x2AVIC is enabled From: Sean Christopherson To: Naveen N Rao Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Suravee Suthikulpanit Content-Type: text/plain; charset="us-ascii" On Wed, Jan 14, 2026, Naveen N Rao wrote: > On Mon, Jan 12, 2026 at 03:28:05PM -0800, Sean Christopherson wrote: > > When allocating the AVIC backing page, only check one of the max AVIC vs. > > x2AVIC ID based on whether or not x2AVIC is enabled. Doing so fixes a bug > > where KVM incorrectly inhibits AVIC if x2AVIC is _disabled_ and any vCPU > > with a non-zero APIC ID is created, as x2avic_max_physical_id is left '0' > > when x2AVIC is disabled. > > > > Fixes: 940fc47cfb0d ("KVM: SVM: Add AVIC support for 4k vCPUs in x2AVIC mode") > > Cc: stable@vger.kernel.org > > Cc: Naveen N Rao (AMD) > > Cc: Suravee Suthikulpanit > > Signed-off-by: Sean Christopherson > > --- > > arch/x86/kvm/svm/avic.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > I think the bad commit is: > f628a34a9d52 ("KVM: SVM: Replace "avic_mode" enum with "x2avic_enabled" boolean") > > ... which introduced x2avic_enabled. No. That commit definitely set a trap for 4k vCPUs support, but there was no functional bug as of that commit. KVM would unnecessarily check @id against X2AVIC_MAX_PHYSICAL_ID, but it's a non-issue because X2AVIC_MAX_PHYSICAL_ID is a constant and greater than AVIC_MAX_PHYSICAL_ID. if ((!x2avic_enabled && id > AVIC_MAX_PHYSICAL_ID) || (id > X2AVIC_MAX_PHYSICAL_ID)) return -EINVAL; So from a "what LTS commits need this fix" perspective, it's just the ones with 940fc47cfb0d.