From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9D5122E975E; Mon, 6 Jul 2026 17:04:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783357476; cv=none; b=VWj4IBXUHrPgWPbXCCF7A+Q4qrbEa8hkA9Y9KBb7tn7LxB3reMH0EeXuxugRptPgNDIzGMOPOhw3pYwEQktxHRFSbZjj5stihoD5w+pgG9t8c7V9YJdwmVXRRjuk/riO2FKLLYVSyxTMgkAN+y3CR5rgZcaXvvXE+SOKoBBqPW0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783357476; c=relaxed/simple; bh=q2bf0hck/kteT/8BiENk5zi92hNnZDmATG4EbRm5dQY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=MNG6Wlnl/KXobjTggWRV5JUz3YGbP2nulao76WITmzSY3BJWSXxd9UJYonTEQfwuPS2YGN/GMjnIt+oWzED2Gq4316OckfLNjzsB8hvA/b9vYiVHpXcy7wiaC10OU4901D70RSRJ2TCabvcYjx3E4cqNGs4TZ3WoDsiwRZFgRV0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gyaaNu0D; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="gyaaNu0D" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E9FE31F000E9; Mon, 6 Jul 2026 17:04:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783357475; bh=REmuzwIaNWYa8LGBVvGUzNpeujzoKq+eMU1Gq13kbjc=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=gyaaNu0DZ3lY+wpZZZxQ/iX7UMQqh0yyWYHoi78HU774kBB/02mxwoerTE+/DOWYp ftBdYzRQvBWyb/29euRzLW3wmTKXWID7tadSd+Nb97HQ7Lw24Q07dQc6tis00rC92/ 8xZPYUxbdNceoDK6j/iBacm63/gI7YctudjwjYi4ceHK5RpWkagVWH7umCwngTYW8+ jtsPBAUVsgiN2pTUkDm/0+7BMFzZCznXpYKvpmV6GwD+WlIHud9o4aaWD5Cu3YNgOe hDWiQNhcSgbvwgEyZXnd/V4YDoYbh9ZojTux/OFUUB/09bWTQe07B9eRAbrcWc2BXO kT/8DfH8xtg5w== Date: Mon, 6 Jul 2026 10:04:33 -0700 From: Oliver Upton To: Akihiko Odaki Cc: Marc Zyngier , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Kees Cook , "Gustavo A. R. Silva" , Paolo Bonzini , Jonathan Corbet , Shuah Khan , Shuah Khan , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, devel@daynix.com, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v8 1/7] KVM: arm64: Disallow vPMU when pPMUs do not cover all CPUs Message-ID: References: <20260706-hybrid-v8-0-de459617b59d@rsg.ci.i.u-tokyo.ac.jp> <20260706-hybrid-v8-1-de459617b59d@rsg.ci.i.u-tokyo.ac.jp> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260706-hybrid-v8-1-de459617b59d@rsg.ci.i.u-tokyo.ac.jp> Hi, On Mon, Jul 06, 2026 at 07:03:24PM +0900, Akihiko Odaki wrote: > Commit ec3eb9ed6081 ("KVM: arm64: PMU: Disallow vPMU on non-uniform > PMUVer") made KVM reject vPMU unless the system-wide PMUVer is usable. > That covers systems where PMUv3 is absent or non-uniform, as well as > systems where IMPDEF PMUv3 sysreg traps are unavailable. > > However, KVM can still accept vPMU when all CPUs uniformly trap PMUv3 > sysregs, but the pPMUs registered with KVM only cover a subset of > possible CPUs. > > Reject vPMU unless the registered pPMUs cover every possible CPU. > This avoids carrying support for partial pPMU coverage into the > fixed-counters-only UAPI introduced later in the series. Doesn't CPU hotplug screw this up? I could online a CPU that doesn't have a PMU after creating the VM. I'd rather just change ARM64_WORKAROUND_PMUV3_IMPDEF_TRAPS to become a system feature. That way any CPU which breaks the system-wide assumption cannot be onlined. Thanks, Oliver