Re: [PATCH 1/1] PCI: Fix bug resulting in double hpmemsize being assigned to MMIO window

[Nicholas Johnson]

On Tue, Nov 12, 2019 at 11:39:53AM +0200, mika.westerberg@xxxxxxxxxxxxxxx wrote:
> On Thu, Nov 07, 2019 at 01:50:57PM +0000, Nicholas Johnson wrote:
> > Currently, the kernel can sometimes assign the MMIO_PREF window
> > additional size into the MMIO window, resulting in extra MMIO additional
> > size, despite the MMIO_PREF additional size being assigned successfully
> > into the MMIO_PREF window.
> > 
> > This happens if in the first pass, the MMIO_PREF succeeds but the MMIO
> > fails. In the next pass, because MMIO_PREF is already assigned, the
> > attempt to assign MMIO_PREF returns an error code instead of success
> > (nothing more to do, already allocated). Hence, the size which is
> > actually allocated, but thought to have failed, is placed in the MMIO
> > window.
> > 
> > Example of problem (more context can be found in the bug report URL):
> > 
> > Mainline kernel:
> > pci 0000:06:01.0: BAR 14: assigned [mem 0x90100000-0xa00fffff] = 256M
> > pci 0000:06:04.0: BAR 14: assigned [mem 0xa0200000-0xb01fffff] = 256M
> > 
> > Patched kernel:
> > pci 0000:06:01.0: BAR 14: assigned [mem 0x90100000-0x980fffff] = 128M
> > pci 0000:06:04.0: BAR 14: assigned [mem 0x98200000-0xa01fffff] = 128M
> > 
> > This was using pci=realloc,hpmemsize=128M,nocrs - on the same machine
> > with the same configuration, with a Ubuntu mainline kernel and a kernel
> > patched with this patch.
> > 
> > The bug results in the MMIO_PREF being added to the MMIO window, which
> > means doubling if MMIO_PREF size = MMIO size. With a large MMIO_PREF,
> > the MMIO window will likely fail to be assigned altogether due to lack
> > of 32-bit address space.
> > 
> > Change find_free_bus_resource() to do the following:
> > - Return first unassigned resource of the correct type.
> > - If none of the above, return first assigned resource of the correct type.
> > - If none of the above, return NULL.
> > 
> > Returning an assigned resource of the correct type allows the caller to
> > distinguish between already assigned and no resource of the correct type.
> > 
> > Rename find_free_bus_resource to find_bus_resource_of_type().
> > 
> > Add checks in pbus_size_io() and pbus_size_mem() to return success if
> > resource returned from find_free_bus_resource() is already allocated.
> > 
> > This avoids pbus_size_io() and pbus_size_mem() returning error code to
> > __pci_bus_size_bridges() when a resource has been successfully assigned
> > in a previous pass. This fixes the existing behaviour where space for a
> > resource could be reserved multiple times in different parent bridge
> > windows.
> > 
> > Link: https://lore.kernel.org/lkml/20190531171216.20532-2-logang@xxxxxxxxxxxx/T/#u
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=203243
> > 
> > Reported-by: Kit Chow <kchow@xxxxxxxxxx>
> > Reported-by: Nicholas Johnson <nicholas.johnson-opensource@xxxxxxxxxxxxxx>
> > Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@xxxxxxxxxxxxxx>
> 
> Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>

Thanks for reviewing.
> 
> Minor nits below.
> 
> > ---
> >  drivers/pci/setup-bus.c | 34 +++++++++++++++++++++++-----------
> >  1 file changed, 23 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> > index e7dbe2170..f97c36a1e 100644
> > --- a/drivers/pci/setup-bus.c
> > +++ b/drivers/pci/setup-bus.c
> > @@ -752,24 +752,32 @@ static void pci_bridge_check_ranges(struct pci_bus *bus)
> >  }
> >  
> >  /*
> > - * Helper function for sizing routines: find first available bus resource
> > - * of a given type.  Note: we intentionally skip the bus resources which
> > - * have already been assigned (that is, have non-NULL parent resource).
> > + * Helper function for sizing routines.
> > + * Assigned resources have non-NULL parent resource.
> > + *
> > + * Return first unassigned resource of the correct type.
> > + * If none of the above, return first assigned resource of the correct type.
> > + * If none of the above, return NULL.
> > + *
> > + * Returning an assigned resource of the correct type allows the caller to
> > + * distinguish between already assigned and no resource of the correct type.
> >   */
> > -static struct resource *find_free_bus_resource(struct pci_bus *bus,
> > -					       unsigned long type_mask,
> > -					       unsigned long type)
> > +static struct resource *find_bus_resource_of_type(struct pci_bus *bus,
> > +						  unsigned long type_mask,
> > +						  unsigned long type)
> >  {
> >  	int i;
> > -	struct resource *r;
> > +	struct resource *r, *r_assigned = NULL;
> 
> Maybe order them
> 
> 	struct resource *r, *r_assigned = NULL;
>  	int i;
Well, technically "r" is used before "i", although "r_assigned" is after 
"i", so I could change it, but it was not in reverse tree order, and I tend 
to leave things as they are. I will consider it.

> 
> >  
> >  	pci_bus_for_each_resource(bus, r, i) {
> >  		if (r == &ioport_resource || r == &iomem_resource)
> >  			continue;
> >  		if (r && (r->flags & type_mask) == type && !r->parent)
> >  			return r;
> > +		if (r && (r->flags & type_mask) == type && !r_assigned)
> > +			r_assigned = r;
> >  	}
> > -	return NULL;
> > +	return r_assigned;
> >  }
> >  
> >  static resource_size_t calculate_iosize(resource_size_t size,
> > @@ -866,14 +874,16 @@ static void pbus_size_io(struct pci_bus *bus, resource_size_t min_size,
> >  			 struct list_head *realloc_head)
> >  {
> >  	struct pci_dev *dev;
> > -	struct resource *b_res = find_free_bus_resource(bus, IORESOURCE_IO,
> > -							IORESOURCE_IO);
> > +	struct resource *b_res = find_bus_resource_of_type(bus, IORESOURCE_IO,
> > +								IORESOURCE_IO);
> >  	resource_size_t size = 0, size0 = 0, size1 = 0;
> >  	resource_size_t children_add_size = 0;
> >  	resource_size_t min_align, align;
> >  
> >  	if (!b_res)
> >  		return;
> 
> I think it may be good to comment here that skip the resources that are
> assigned (->parent != NULL).

Something like

/* If resource is already assigned, nothing more to do. */

OR

/* If resource is already assigned (->parent != NULL), nothing more to do */

OR something else?

> 
> > +	if (b_res->parent)
> > +		return;
> >  
> >  	min_align = window_alignment(bus, IORESOURCE_IO);
> >  	list_for_each_entry(dev, &bus->devices, bus_list) {
> > @@ -978,7 +988,7 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
> >  	resource_size_t min_align, align, size, size0, size1;
> >  	resource_size_t aligns[18]; /* Alignments from 1MB to 128GB */
> >  	int order, max_order;
> > -	struct resource *b_res = find_free_bus_resource(bus,
> > +	struct resource *b_res = find_bus_resource_of_type(bus,
> >  					mask | IORESOURCE_PREFETCH, type);
> >  	resource_size_t children_add_size = 0;
> >  	resource_size_t children_add_align = 0;
> > @@ -986,6 +996,8 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
> >  
> >  	if (!b_res)
> >  		return -ENOSPC;
> 
> Ditto.

Same as above, will use the same comment if I do one.

> 
> > +	if (b_res->parent)
> > +		return 0;
> >  
> >  	memset(aligns, 0, sizeof(aligns));
> >  	max_order = 0;
> > -- 
> > 2.23.0

Thanks,

Kind regards,
Nicholas