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 B46C7322C88; Fri, 2 Oct 2026 23:47:51 +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=1790984872; cv=none; b=exWdxld2uzsU0+Qi+Qp4mJOex96+KYaA4X2AFHHSheD3xSHRj78cxYLroIMPJ1J9pzV3v54dh08eZCGJ5xGrSNEIxtOyReD5KylEgnSDzKmBYZ/Q8bVuevVMkSuBvAk11keQywqnl8z65E74FWqRGYRVV1k20gZYm6KrcKw6WVE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790984872; c=relaxed/simple; bh=PvstLQce3TC1gPzev1tDM+Cp+11UbN16I70iVrQ8qNc=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; b=ezjq/YCSOz3fuSfXMdF0IXd1GnRQzpXY44fSY8QGE4H8q4v/tTo81CCx53c9ufMBHFvTxJjw6Yp/Vm3ET/dtX74MAKlq+627AxyLaARCt567B/MxyaR1K7Fy10XHrDBQtO/qUTVO76hzHacJEmIMM7XkdOka4pD4eGDurYGnIuc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PRabq4VU; 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="PRabq4VU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0362B1F000FF; Fri, 2 Oct 2026 23:47:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790984871; bh=mN4BUccomOxQP6dbLy3uvQNSnAAqcoTSVXqAPXIymNY=; h=Date:From:To:Cc:Subject:In-Reply-To; b=PRabq4VU4ZLHFbxtawTgO6RXWIeLXb6I4LbdyVZboLOfbiCesxv0UKv8vK1UIytj1 wXmTfmTN1Bu1A7mkDrT1Z8OK5IVtSYeeaYlp8UJUa/nVXBAcTTByRRI3zpknkCtAyy y7ukLW4ydY6pn1zVUQmxQkLoCJi4oNdForZ0I1xz1dVX1L+rX1k7cmYd21/4KLwjkg /uaZ54lo+pyKodDxeYdvVbzeC5NCiEr2EBkxGlHTsSP7pbRhpjEsWEdg1S39TiNziT JmYpQP8SbG/27yiI1AP8MMJ7YKil7aeLBo+xEpAiBy1sYi16BcGx3oOdwvHOocSYsI vy3G8KKEPXPmQ== Date: Fri, 2 Oct 2026 18:47:49 -0500 From: Bjorn Helgaas To: Alex Williamson Cc: Jose Ignacio Tornos Martinez , bhelgaas@google.com, mani@kernel.org, jjohnson@kernel.org, linux-pci@vger.kernel.org, linux-wireless@vger.kernel.org, ath11k@lists.infradead.org, ath12k@lists.infradead.org, mhi@lists.linux.dev, linux-kernel@vger.kernel.org, Jason Gunthorpe Subject: Re: [PATCH v14 0/2] PCI: Add device-specific reset for Qualcomm devices Message-ID: <20261002234749.GA411439@bhelgaas> Precedence: bulk X-Mailing-List: linux-kernel@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: <20261002170949.59c3d47a@shazbot.org> On Fri, Oct 02, 2026 at 05:09:49PM -0600, Alex Williamson wrote: > On Fri, 2 Oct 2026 16:40:58 -0500 > Bjorn Helgaas wrote: > > > [cc->to: Alex, +cc Jason] > > > > On Thu, Sep 17, 2026 at 09:16:49AM +0200, Jose Ignacio Tornos Martinez wrote: > > > Some Qualcomm PCIe devices (WCN6855, WCN7850 WLAN; SDX62/SDX65 modems) > > > lack working reset methods for VFIO passthrough scenarios. These devices > > > have no FLR capability, advertise NoSoftRst+ (blocking PM reset), and have > > > broken bus reset (addressed by quirk_no_bus_reset, merged for v7.2). > > > > Specifically, 6a4f64c3a3ad ("PCI: Avoid SBR for Qualcomm > > WCN6855/WCN7850 WiFi, SDX62/SDX65 modems"). I don't know what the > > behavior was prior to that commit. I suppose it was something > > obvious? > > > > > VFIO attempts to reset devices on every reassignment: > > > - For the listed modems, without a proper reset capability, these devices > > > never successfully initialize even on first VM assignment. > > > - For the listed WLAN devices, without a working reset method, the attempt > > > fails. On clean VM shutdown, the guest driver properly deinitializes the > > > device via .shutdown/.remove callbacks, leaving it in a usable state despite > > > the failed reset. However, on unclean VM termination (crash, force-off), the > > > guest driver callbacks are not triggered, the device remains in an undefined > > > state (DMA active, interrupts enabled, etc.), and without a working reset it > > > cannot be reused. > > > > So IIUC, prior to these patches, these devices were functional when > > passed through to several successive guests as long as the guests shut > > down cleanly, but the resets done by VFIO didn't work, so the host > > couldn't enforce isolation between those guests. > > > > If true, I propose updating the commit logs to emphasize the lack of > > isolation and de-emphasize the VM clean shutdown vs crash behavior, > > e.g.: > > > > Resets of this device always failed prior to this commit, so VFIO on > > the host could not enforce isolation between successive passthrough > > users. > > > > If a guest driver deinitialized the device, it may have been > > functional if passed through to a subsequent guest, despite the lack > > of isolation. Otherwise the device may have been left in an > > undefined state (e.g., DMA and interrupts active) and unusable. > > > > It would also be great to have Alex's ack here. > > Yes, aiui it's an isolation and repeatability issue. In fact, without > knowing what's actually stored in the hardware, I'd suspect it's more > the latter and the testing proves that. Mani is really the one > vouching for it from the hardware, isolation perspective. > > Standard reset methods have never worked on these devices and that's > now evident by the quirks that disable them for these devices. This > fills the remaining gap by providing device specific resets for the same > hardware. > > Both patches should properly reference the quirk_no_bus_reset commit, > but otherwise these look correct, afaict. > > Acked-by: Alex Williamson Thanks, Alex!