From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta1.migadu.com (out-179.mta1.migadu.com [95.215.58.179]) (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 411BE1292F3 for ; Tue, 23 Jan 2024 19:00:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706036431; cv=none; b=YkJpt0aF7RtHty3ePTfcVOU0iiIUvF36iMG0aqjqsYOxVYWE7pK3NQwvn1+yCeoQEk9PqPuzAXA/h7DdcFLkGCSTfSSfCMjYIcLZ02y8cksANktjpy0qP78lWv6drJv3306GS7klasFLFa7NngZIjgSqo1l7S/qZuyWPDRtIXvU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706036431; c=relaxed/simple; bh=mQE00aWkgMtqv7svnhbWuPmspbA1rLHb4HEe2MN8pW0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=m3FLg9f4hHIa8BPaKH2pc6dvw5UPnIZvuPENlkpwwNsHB8bJPXiu8tkV7APlWIpQtFBQjQtLAtJf3yaDO8K2+z5T/cQFPdwA1w2A7QjxW4bHPq0mIbZ7j7kua7w8/F9acW9vUuIIc04KWDB534IiXIQDO2ePzbmox/AM5kT/7uA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=Slc3bqyG; arc=none smtp.client-ip=95.215.58.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="Slc3bqyG" Date: Tue, 23 Jan 2024 19:00:23 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1706036427; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=eYMck5L6uue4zc3PPO2ctKiLd5MW2oLCukny7sBp2yA=; b=Slc3bqyGnQbls7pi/u8B+xOBhLft1gJPx7L42fMBMqeCXrBmNvPKs+KsXRwaH9jUlwA7ry DI7wJgeioGokPC+o6du6iGrX71qjPvczafhmDNdTEOL8C+fMY9q+unxab9XJS5+2IbC4G+ QXf3ed9n0ZqSo5P768GQLkR4RIM+jcA= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: James Morse Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, Marc Zyngier , Suzuki K Poulose , Zenghui Yu Subject: Re: [PATCH v2 0/4] KVM: arm64: Hide unsupported MPAM from the guest Message-ID: References: <20231207150804.3425468-1-james.morse@arm.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT On Fri, Jan 19, 2024 at 05:15:59PM +0000, James Morse wrote: [...] > > We've already done something similar to hide our mistakes with IMP DEF > > PMU versions in commit f90f9360c3d7 ("KVM: arm64: Rewrite IMPDEF PMU > > version as NI"), and I think MPAM may be a good candidate for something > > similar. > > As there is precedent, I feel less dirty doing that! > > This also solves the problem of the VMM re-writing the broken value after the vCPU has > started running, and getting a surprise error. A weird side effect of doing this would be > you can write MPAM=1 on A53 and KVM will ignore it, I don't want user-space to start > relying on that! I'll add a final-cap check so this can only be ignored on hardware that > actually has MPAM, and could have been exposed to the bug. Ah, good idea. I probably should've done something similar in the PMU case. -- Thanks, Oliver