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 3899F3A759D; Sun, 11 Oct 2026 05:47:05 +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=1791697627; cv=none; b=mhLsCAHp4tm8Ai0vK+kX2zk55+ABolErsmjMyL8N5qru+M62cRvRDf868qBMrKevYFkAnLxg45J26k0/zFRrROIA62ugUF4fKwG5jfHRVV6vDJ+aogKAtT+eoIA3IdwphdJCCSCw65jEtotls16i9CkwMi4lP5uHIJYCY4HsaXk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791697627; c=relaxed/simple; bh=3VNnIGVBv9EL0BAqLp7Vak8V4WA/96/zgoDpeAl9MhY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=lIjQBPjRjsDA6lIuw9kLi15CacmDd0Bd+d4upY7rcvsV0Wv2mm9OclbEv/r9X89y47+a5URg5WYSJfX7jYh9cvWcXHjPDEFxk50ktFaPQfMCHKeKGg+QRTj1J57hHN7MXcd9tpSmKBOMk3PCWyM58VAdsHaJtshueW68ICKKhKw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ktbtfv6T; 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="Ktbtfv6T" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1D4141F0089B; Sun, 11 Oct 2026 05:47:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791697625; bh=V26Y85Vt2vGB2apj7LD4RMbjX6GtqdMPTO8AtJrxgxY=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Ktbtfv6TUq5tx7CgLuP550bk8DrnLJRr0QNnhGWxbJEUPy3STpWo71Ce1u0DEW6bu asV3ptTx4SWo+afU+TN/wUIRni+1g38rNtNZkLOKWNg/sXjb/4caDeFDMSpe3ggflW Qw2OesF5eRno/VVJ52Yiv0IeR6klp/mBC/5BAnQo5KqMM0R2V9l3Nss7gv/5OzfdnE zqxic6xSIgMQgkzTBhi/ymM0/9/qLr0uwXhjoWhlvF7SpBhVQZ99Jo7T5Kg6aompXw MW7mC2xvb8+H9kcoy8OcKnrhmV+HTHqlzEMmanf9p29/eU1LbpYakmeUrBXLNOI4Yr 9M5WpWt94CjlQ== Date: Sun, 11 Oct 2026 08:47:00 +0300 From: Leon Romanovsky To: "Popov, Pavel E" Cc: Bjorn Helgaas , Jim Chow , Bjorn Helgaas , Logan Gunthorpe , Radu Rugina , Alexey Makhalov , Wei Liu , Michael Kelley , Lukas Wunner , Nathan Ciobanu , "bcm-kernel-feedback-list@broadcom.com" , "virtualization@lists.linux.dev" , "linux-hyperv@vger.kernel.org" , "linux-pci@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 0/2] PCI/P2PDMA: Allow P2PDMA in VMware and Hyper-V guests on Intel hosts Message-ID: <20261011054700.GF11438@unreal> References: <20261009154034.82321-1-pavel.e.popov@intel.com> <20261009165833.GA991924@bhelgaas> <20261009180847.GD11438@unreal> <20261009184923.GE11438@unreal> Precedence: bulk X-Mailing-List: linux-pci@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: On Fri, Oct 09, 2026 at 07:13:31PM +0000, Popov, Pavel E wrote: > Leon, > > Understood on all points, and I agree HMAT is the proper fix. We discussed > it with Lukas Wunner as well. Exposing HMAT is on the hypervisor side; Jim > Chow from VMware can speak to their plans. Even once HMAT lands in Linux, > it only helps guests after the hypervisors add support for it. > > The key point for us is that today there is no path at all for > passthrough devices on VMware or Hyper-V, and that is what this patch > addresses. We reviewed it with VMware and aligned on this approach for the > guest in the meantime. This does not change the fact that the patch causes unpredictable behavior for P2P devices in the guest. Sometimes it works; other times, devices that previously worked may be classified as P2P-capable and will stop. > > Is there anything you would recommend to make the series acceptable as an > interim? Help Lukas and Mahesh succeed in their work. Thanks