linux-kernel - Re: [PATCH v3 15/15] Drivers: hv: Add modules to expose /dev/mshv to VMMs running on Hyper-V

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Date:   Sat, 23 Sep 2023 20:58:00 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arch@...r.kernel.org, patches@...ts.linux.dev,
        mikelley@...rosoft.com, kys@...rosoft.com, wei.liu@...nel.org,
        haiyangz@...rosoft.com, decui@...rosoft.com,
        apais@...ux.microsoft.com, Tianyu.Lan@...rosoft.com,
        ssengar@...ux.microsoft.com, mukeshrathor@...rosoft.com,
        stanislav.kinsburskiy@...il.com, jinankjain@...ux.microsoft.com,
        vkuznets@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        will@...nel.org, catalin.marinas@....com
Subject: Re: [PATCH v3 15/15] Drivers: hv: Add modules to expose /dev/mshv to
 VMMs running on Hyper-V

Greg, thank you for looking at the code.

On Sat, Sep 23, 2023 at 09:56:13AM +0200, Greg KH wrote:
> On Fri, Sep 22, 2023 at 11:38:35AM -0700, Nuno Das Neves wrote:
> > +static int __init mshv_vtl_init(void)
> > +{
> > +	int ret;
> > +
> > +	tasklet_init(&msg_dpc, mshv_vtl_sint_on_msg_dpc, 0);
> > +	init_waitqueue_head(&fd_wait_queue);
> > +
> > +	if (mshv_vtl_get_vsm_regs()) {
> > +		pr_emerg("%s: Unable to get VSM capabilities !!\n", __func__);
> > +		BUG();
> > +	}
> 
> 
> So you crash the whole kernel if someone loads this module on a non-mshv
> system?
> 
> That seems quite excessive and hostile :(
> 

I agree this can be more lenient. It should be safe to just return an
error code (ENODEV) and let user space decide the next action.

Saurabh, let me know what you think.

Thanks,
Wei.

> Or am I somehow reading this incorrectly?
> 
> thanks,
> 
> greg k-h
>