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Message-ID: <d42a3430-a365-4fd3-bfd4-efa567f777a8@codeaurora.org> Date: Thu, 7 Dec 2017 10:44:04 -0500 From: "Leeder, Neil" <nleeder@...eaurora.org> To: Will Deacon <will.deacon@....com> Cc: nleeder@...eaurora.org, Mark Rutland <mark.rutland@....com>, linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, Mark Langsdorf <mlangsdo@...hat.com>, Mark Salter <msalter@...hat.com>, Jon Masters <jcm@...hat.com>, Timur Tabi <timur@...eaurora.org>, Mark Brown <broonie@...nel.org> Subject: Re: [PATCH] perf: qcom_l2_pmu: don't allow guest access On 12/7/2017 8:38 AM, Will Deacon wrote: > On Wed, Dec 06, 2017 at 04:19:24PM -0500, Leeder, Neil wrote: >> On 12/6/2017 11:11 AM, Mark Rutland wrote: >>> On Wed, Dec 06, 2017 at 10:55:33AM -0500, Neil Leeder wrote: >>>> Guests cannot access IMPDEF system registers, which are used >>>> by this driver. Disable the driver if it's running in a guest VM. >>>> >>>> Signed-off-by: Neil Leeder <nleeder@...eaurora.org> >>>> --- >>>> drivers/perf/qcom_l2_pmu.c | 4 ++++ >>>> 1 file changed, 4 insertions(+) >>> >>> I'm a little confused by this. Why is this hypervisor providing a >>> QCOM8130 device to the guest that it cannot use? >>> >>> Could you elaborate on what's going on? >>> >> >> While there's an argument that the guest shouldn't be loading the driver >> in the first place, we can't control everyone's guest configuration or what >> their hypervisor does. > > Ok, but why is the hypervisor advertising a device that effectively doesn't > exist? Most drivers trust the firmware tables they are given, so this makes > it sound like we should start annotating all drivers for devices that we > don't expect to see in a guest with is_hyp_mode_available() checks. > > That doesn't feel quite right to me. Hi Will, I suspect that most mis-configured drivers don't fail until they're used, or are otherwise Mostly Harmless. The problem here is that this driver uses IMPDEF system registers in its init, and I'd guess only a minority of drivers do that. So it crashed the kernel with an illegal instruction on boot. I'm trying to be a good citizen here and not allow my driver to stop a kernel from booting because someone misconfigured something out of my control. Neil -- Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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