Subject: Re: [PATCH v4 3/7] PCI: Separate VF BAR updates from standard BAR updates

From: Gavin Shan <[email-masked]>
Date: Wed, 30 Nov 2016 10:20:28 +1100

On Tue, Nov 29, 2016 at 08:48:26AM -0600, Bjorn Helgaas wrote:
>On Tue, Nov 29, 2016 at 03:55:46PM +1100, Gavin Shan wrote:
>> On Mon, Nov 28, 2016 at 10:15:06PM -0600, Bjorn Helgaas wrote:
>> >Previously pci_update_resource() used the same code path for updating
>> >standard BARs and VF BARs in SR-IOV capabilities.
>> >
>> >Split the VF BAR update into a new pci_iov_update_resource() internal
>> >interface, which makes it simpler to compute the BAR address (we can get
>> >rid of pci_resource_bar() and pci_iov_resource_bar()).
>> >
>> >This patch:
>> >
>> >  - Renames pci_update_resource() to pci_std_update_resource(),
>> >  - Adds pci_iov_update_resource(),
>> >  - Makes pci_update_resource() a wrapper that calls the appropriate one,
>> >
>> >No functional change intended.
>> >
>> >Signed-off-by: Bjorn Helgaas <[email-masked]>
>> 
>> With below minor comments fixed:
>> 
>> Reviewed-by: Gavin Shan <[email-masked]>
>> 
>> >---
>> > drivers/pci/iov.c       |   49 +++++++++++++++++++++++++++++++++++++++++++++++
>> > drivers/pci/pci.h       |    1 +
>> > drivers/pci/setup-res.c |   13 +++++++++++-
>> > 3 files changed, 61 insertions(+), 2 deletions(-)
>> >
>> >diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>> >index d41ec29..d00ed5c 100644
>> >--- a/drivers/pci/iov.c
>> >+++ b/drivers/pci/iov.c
>> >@@ -571,6 +571,55 @@ int pci_iov_resource_bar(struct pci_dev *dev, int resno)
>> > 		4 * (resno - PCI_IOV_RESOURCES);
>> > }
>> >
>> >+/**
>> >+ * pci_iov_update_resource - update a VF BAR
>> >+ * @dev: the PCI device
>> >+ * @resno: the resource number
>> >+ *
>> >+ * Update a VF BAR in the SR-IOV capability of a PF.
>> >+ */
>> >+void pci_iov_update_resource(struct pci_dev *dev, int resno)
>> >+{
>> >+	struct pci_sriov *iov = dev->is_physfn ? dev->sriov : NULL;
>> >+	struct resource *res = dev->resource + resno;
>> >+	int vf_bar = resno - PCI_IOV_RESOURCES;
>> >+	struct pci_bus_region region;
>> >+	u32 new;
>> >+	int reg;
>> >+
>> >+	/*
>> >+	 * The generic pci_restore_bars() path calls this for all devices,
>> >+	 * including VFs and non-SR-IOV devices.  If this is not a PF, we
>> >+	 * have nothing to do.
>> >+	 */
>> >+	if (!iov)
>> >+		return;
>> >+
>> >+	/*
>> >+	 * Ignore unimplemented BARs, unused resource slots for 64-bit
>> >+	 * BARs, and non-movable resources, e.g., those described via
>> >+	 * Enhanced Allocation.
>> >+	 */
>> >+	if (!res->flags)
>> >+		return;
>> >+
>> >+	if (res->flags & IORESOURCE_UNSET)
>> >+		return;
>> >+
>> >+	if (res->flags & IORESOURCE_PCI_FIXED)
>> >+		return;
>> >+
>> >+	pcibios_resource_to_bus(dev->bus, &region, res);
>> >+	new = region.start;
>> >+
>> 
>> The bits indicating the BAR's property (e.g. memory, IO etc) are missed in @new.
>
>Hmm, yes.  I omitted those because those bits are supposed to be
>read-only, per spec (PCI r3.0, sec 6.2.5.1).  But I guess it would be
>more conservative to keep them, and this shouldn't be needlessly
>different from pci_std_update_resource().
>

Yeah, Agree.

>However, I don't think this code in pci_update_resource() is obviously
>correct:
>
>  new = region.start | (res->flags & PCI_REGION_FLAG_MASK);
>
>PCI_REGION_FLAG_MASK is 0xf.  For memory BARs, bits 0-3 are read-only
>property bits.  For I/O BARs, bits 0-1 are read-only and bits 2-3 are
>part of the address, so on the face of it, the above could corrupt two
>bits of an I/O address.
>
>It's true that decode_bar() initializes flags correctly, using
>PCI_BASE_ADDRESS_IO_MASK for I/O BARs and PCI_BASE_ADDRESS_MEM_MASK
>for memory BARs, but it would take a little more digging to be sure
>that we never set bits 2-3 of flags for an I/O resource elsewhere.
>

The BAR's property bits are probed from device-tree, not hardware
on some platforms (e.g. pSeries). Also, there is only one (property)
bit if it's a ROM BAR. So more check as below might be needed because
the code (without the enhancement) should also work fine.

>How about this in pci_std_update_resource():
>
>        pcibios_resource_to_bus(dev->bus, &region, res);
>        new = region.start;
>
>        if (res->flags & IORESOURCE_IO) {
>                mask = (u32)PCI_BASE_ADDRESS_IO_MASK;
>                new |= res->flags & ~PCI_BASE_ADDRESS_IO_MASK;
>        } else {
>                mask = (u32)PCI_BASE_ADDRESS_MEM_MASK;
>                new |= res->flags & ~PCI_BASE_ADDRESS_MEM_MASK;
>        }
>

	if (res->flags & IORESOURCE_IO) {
		mask = (u32)PCI_BASE_ADDRESS_IO_MASK;
		new |= res->flags & ~PCI_BASE_ADDRESS_IO_MASK;
	} else if (resno < PCI_ROM_RESOURCE) {
		mask = (u32)PCI_BASE_ADDRESS_MEM_MASK;
		new |= res->flags & ~PCI_BASE_ADDRESS_MEM_MASK;
	} else if (resno == PCI_ROM_RESOURCE) {
		mask = ~((u32)IORESOURCE_ROM_ENABLE);
		new |= res->flags & IORESOURCE_ROM_ENABLE);
	} else {
		dev_warn(&dev->dev, "BAR#%d out of range\n", resno);
		return;
	}

>and this in pci_iov_update_resource():
>
>        pcibios_resource_to_bus(dev->bus, &region, res);
>        new = region.start;
>        new |= res->flags & ~PCI_BASE_ADDRESS_MEM_MASK;
>
>It shouldn't fix anything, but I think it is more obvious that we
>can't corrupt bits 2-3 of an I/O BAR.
>

Agree and the this part of changes look good to me.

>> >+	reg = iov->pos + PCI_SRIOV_BAR + 4 * vf_bar;
>> >+	pci_write_config_dword(dev, reg, new);
>> >+	if (res->flags & IORESOURCE_MEM_64) {
>> >+		new = region.start >> 16 >> 16;
>> 
>> I think it was copied from pci_update_resource(). Why we can't just have "new = region.start >> 32"? 
>
>Right; I did copy this from pci_update_resource().  The changelog from
>cf7bee5a0bf2 ("[PATCH] Fix restore of 64-bit PCI BAR's") says "Also
>make sure to write high bits - use "x >> 16 >> 16" (rather than the
>simpler ">> 32") to avoid warnings on 32-bit architectures where we're
>not going to have any high bits."
>
>I didn't take the time to revalidate whether that's still applicable.
>

Ah, I see. I think we still need this on 32-bits systems.

>> >+void pci_update_resource(struct pci_dev *dev, int resno)
>> >+{
>> >+	if (resno <= PCI_ROM_RESOURCE)
>> >+		pci_std_update_resource(dev, resno);
>> >+#ifdef CONFIG_PCI_IOV
>> >+	else if (resno >= PCI_IOV_RESOURCES && resno < PCI_IOV_RESOURCE_END)
>> 
>> The last BAR is missed:
>> 
>> 	else if (resno >= PCI_IOV_RESOURCES && resno <= PCI_IOV_RESOURCE_END)
>
>Ah, right, thanks!
>
>> >+		pci_iov_update_resource(dev, resno);
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