linux-kernel - RE: [PATCH V6 7/8] Drivers: hv: vmbus: Add SNP support for VMbus channel initiate message

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Date:   Mon, 4 Oct 2021 02:39:51 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     Tianyu Lan <ltykernel@...il.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
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        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
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        "brijesh.singh@....com" <brijesh.singh@....com>,
        "jroedel@...e.de" <jroedel@...e.de>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
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CC:     "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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        vkuznets <vkuznets@...hat.com>,
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        "hch@....de" <hch@....de>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "joro@...tes.org" <joro@...tes.org>,
        "parri.andrea@...il.com" <parri.andrea@...il.com>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>
Subject: RE: [PATCH V6 7/8] Drivers: hv: vmbus: Add SNP support for VMbus
 channel initiate message

From: Tianyu Lan <ltykernel@...il.com> Sent: Saturday, October 2, 2021 7:40 AM
> 
> 
> On 10/2/2021 9:26 PM, Michael Kelley wrote:
> >> @@ -303,10 +365,26 @@ void vmbus_disconnect(void)
> >>   		vmbus_connection.int_page = NULL;
> >>   	}
> >>
> >> -	hv_free_hyperv_page((unsigned long)vmbus_connection.monitor_pages[0]);
> >> -	hv_free_hyperv_page((unsigned long)vmbus_connection.monitor_pages[1]);
> >> -	vmbus_connection.monitor_pages[0] = NULL;
> >> -	vmbus_connection.monitor_pages[1] = NULL;
> >> +	if (hv_is_isolation_supported()) {
> >> +		memunmap(vmbus_connection.monitor_pages[0]);
> >> +		memunmap(vmbus_connection.monitor_pages[1]);
> > The matching memremap() calls are made in vmbus_connect() only in the
> > SNP case.  In the non-SNP case, monitor_pages and monitor_pages_original
> > are the same, so you would be doing an unmap, and then doing the
> > set_memory_encrypted() and hv_free_hyperv_page() using an address
> > that is no longer mapped, which seems wrong.   Looking at memunmap(),
> > it might be a no-op in this case, but even if it is, making them conditional
> > on the SNP case might be a safer thing to do, and it would make the code
> > more symmetrical.
> >
> 
> Yes, memumap() does nothing is the non-SNP CVM and so I didn't check CVM
> type here. I will add the check in the next version.
> 
> Thanks.
> 

I would also be OK with just adding a comment to that effect, just so someone
looking at the code in the future understands that there's not a problem.
Your call.

Michael