netdev - RE: Hyperv netvsc - regression for 32-PAE kernel

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Date:   Fri, 3 May 2019 19:58:13 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Michael Kelley <mikelley@...rosoft.com>,
        Juliana Rodrigueiro <juliana.rodrigueiro@...ra2net.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: Hyperv netvsc - regression for 32-PAE kernel

> From: linux-hyperv-owner@...r.kernel.org
> <linux-hyperv-owner@...r.kernel.org> On Behalf Of Michael Kelley
> Sent: Thursday, May 2, 2019 3:24 PM
> To: Juliana Rodrigueiro <juliana.rodrigueiro@...ra2net.com>;
> linux-hyperv@...r.kernel.org
> Cc: netdev@...r.kernel.org
> Subject: RE: Hyperv netvsc - regression for 32-PAE kernel
> 
> From: Juliana Rodrigueiro <juliana.rodrigueiro@...ra2net.com> Sent: Thursday,
> May 2, 2019 9:14 AM
> >
> > So I got to the following commit:
> >
> > commit 6ba34171bcbd10321c6cf554e0c1144d170f9d1a
> > Author: Michael Kelley <mikelley@...rosoft.com>
> > Date:   Thu Aug 2 03:08:24 2018 +0000
> >
> >     Drivers: hv: vmbus: Remove use of slow_virt_to_phys()
> >
> >     slow_virt_to_phys() is only implemented for arch/x86.
> >     Remove its use in arch independent Hyper-V drivers, and
> >     replace with test for vmalloc() address followed by
> >     appropriate v-to-p function. This follows the typical
> >     pattern of other drivers and avoids the need to implement
> >     slow_virt_to_phys() for Hyper-V on ARM64.
> >
> >     Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
> >     Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> >     Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> >
> > The catch is that slow_virt_to_phys has a special trick implemented in order
> > to keep specifically 32-PAE kernel working, it is explained in a comment
> > inside the function.
> >
> > Reverting this commit makes the kernel 4.19 32-bit PAE work again. However
> I
> > believe a better solution might exist.
> >
> > Comments are very much appreciated.
> >
> 
> Julie -- thanks for tracking down the cause of the issue.  I'll try to
> look at this tomorrow and propose a solution.
> 
> Michael Kelley

Hi Juliana,
Can you please try the below one-line patch? 

It should fix the issue.

Thanks,
-- Dexuan

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 23381c4..aaaee5f 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -38,7 +38,7 @@

 static unsigned long virt_to_hvpfn(void *addr)
 {
-       unsigned long paddr;
+       phys_addr_t paddr;

        if (is_vmalloc_addr(addr))
                paddr = page_to_phys(vmalloc_to_page(addr)) +