linux-kernel - Re: [PATCH v2 1/2] PCI: hv: Replace hv_vp_set with hv

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Message-ID: <20190213115044.GB25260@e107981-ln.cambridge.arm.com>
Date:   Wed, 13 Feb 2019 11:50:44 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     "m.maya.nakamura" <m.maya.nakamura@...il.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "apw@...onical.com" <apw@...onical.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "driverdev-devel@...uxdriverproject.org" 
        <driverdev-devel@...uxdriverproject.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        vkuznets <vkuznets@...hat.com>,
        "marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>
Subject: Re: [PATCH v2 1/2] PCI: hv: Replace hv_vp_set with hv_vpset

On Wed, Feb 13, 2019 at 02:20:29AM +0000, Michael Kelley wrote:
> From: Lorenzo Pieralisi <lorenzo.pieralisi@....com>  Sent: Tuesday, February 12, 2019 8:35 AM
> >
> > On Mon, Jan 28, 2019 at 09:49:32PM -0800, Maya Nakamura wrote:
> > > On Sun, Jan 27, 2019 at 05:11:48AM +0000, Michael Kelley wrote:
> > > > From: Maya Nakamura <m.maya.nakamura@...il.com>  Sent: Saturday, January 26,
> > 2019 12:52 AM
> > > > >
> > > > > Remove a duplicate definition of VP set (hv_vp_set) and use the common
> > > > > definition (hv_vpset) that is used in other places.
> > > > >
> > > > > Change the order of the members in struct hv_pcibus_device so that the
> > > > > declaration of retarget_msi_interrupt_params is the last member. Struct
> > > > > hv_vpset, which contains a flexible array, is nested two levels deep in
> > > > > struct hv_pcibus_device via retarget_msi_interrupt_params.
> > > > >
> > > > > Add a comment that retarget_msi_interrupt_params should be the last member
> > > > > of struct hv_pcibus_device.
> > > > >
> > > > > Signed-off-by: Maya Nakamura <m.maya.nakamura@...il.com>
> > > > > ---
> > > > > Change in v2:
> > > > > - None
> > > > >
> > > >
> > > > Right -- there was no code change.  But it's customary to note that
> > > > you updated the commit message.
> > > >
> > > Thank you for your feedback. I will edit the change log in v3.
> > >
> > > > Reviewed-by:  Michael Kelley <mikelley@...rosoft.com>
> > 
> > Are you really sure there is no behavioural change ? What piece of
> > code allocates hv_vpset.bank_contents[] memory with this patch applied ?
> > 
> > I suspect the current code does not use hv_vpset for this specific
> > reason, ie allocate struct hv_vp_set.masks array memory statically.
> > 
> 
> There is indeed no behavior change.   A full page of memory is
> allocated in hv_pci_probe() so that we can be sure that the Hyper-V
> hypercall arguments don't cross a page boundary.   This page allows
> more than enough space for the hv_vpset.bank_contents[] to grow
> as needed (with one bit allocated in the masks for up to the limit
> of 8192 CPUs allowed by Linux).   A flexible array is used because
> the hv_vpset structure is also used in some MMU hypercalls that
> have two variable size arrays.

I see, thanks for explaining.

Lorenzo