Re: [PATCH v2 1/2] PCI: hv: Replace hv_vp_set with hv_vpset

From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Michael Kelley <mikelley@microsoft.com>
Cc: "m.maya.nakamura" <m.maya.nakamura@gmail.com>,
	"bhelgaas@google.com" <bhelgaas@google.com>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	KY Srinivasan <kys@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	"olaf@aepfle.de" <olaf@aepfle.de>,
	"apw@canonical.com" <apw@canonical.com>,
	"jasowang@redhat.com" <jasowang@redhat.com>,
	Sasha Levin <Alexander.Levin@microsoft.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"driverdev-devel@linuxdriverproject.org" 
	<driverdev-devel@linuxdriverproject.org>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	vkuznets <vkuznets@redhat.com>,
	"marcelo.cerri@canonical.com" <marcelo.cerri@canonical.com>
Subject: Re: [PATCH v2 1/2] PCI: hv: Replace hv_vp_set with hv_vpset
Date: Wed, 13 Feb 2019 11:50:44 +0000	[thread overview]
Message-ID: <20190213115044.GB25260@e107981-ln.cambridge.arm.com> (raw)
In-Reply-To: <DM5PR2101MB091868E19484F7DCD8C69171D7660@DM5PR2101MB0918.namprd21.prod.outlook.com>

On Wed, Feb 13, 2019 at 02:20:29AM +0000, Michael Kelley wrote:
> From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.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@gmail.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@gmail.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@microsoft.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