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    SubjectRe: [PATCH] PCI: Check value of resource alignment before using __ffs
    On 21/04/22 01:41PM, Leon Romanovsky wrote:
    > On Thu, Apr 22, 2021 at 03:13:23PM +0530, Amey Narkhede wrote:
    > > On 21/04/22 09:43AM, Leon Romanovsky wrote:
    > > > On Thu, Apr 22, 2021 at 12:17:47AM +0530, Amey Narkhede wrote:
    > > > > Return value of __ffs is undefined if no set bit exists in
    > > > > its argument. This indicates that the associated BAR has
    > > > > invalid alignment.
    > > > >
    > > > > Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com>
    > > > > ---
    > > > > drivers/pci/setup-bus.c | 5 +++++
    > > > > 1 file changed, 5 insertions(+)
    > > > >
    > > > > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
    > > > > index 2ce636937c6e..44e8449418ae 100644
    > > > > --- a/drivers/pci/setup-bus.c
    > > > > +++ b/drivers/pci/setup-bus.c
    > > > > @@ -1044,6 +1044,11 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
    > > > > * resources.
    > > > > */
    > > > > align = pci_resource_alignment(dev, r);
    > > > > + if (!align) {
    > > > > + pci_warn(dev, "BAR %d: %pR has bogus alignment\n",
    > > > > + i, r);
    > > > > + continue;
    > > > > + }
    > > >
    > > > I see that you copied it from pdev_sort_resources(), but it is
    > > > incorrect change, see how negative order is handled and later
    > > > ARRAY_SIZE() check.
    > > >
    > > > Thanks
    > > >
    > > Is it guaranteed that it will return value which will result
    > > in negative value or >= ARRAY_SIZE? Comment on __ffs says value
    > > is undefined for 0 that means it could be anything or am I missing
    > > something?
    >
    > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
    > index 2ce636937c6e..ce5380bdd2fd 100644
    > --- a/drivers/pci/setup-bus.c
    > +++ b/drivers/pci/setup-bus.c
    > @@ -1044,10 +1044,11 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
    > * resources.
    > */
    > align = pci_resource_alignment(dev, r);
    > - order = __ffs(align) - 20;
    > - if (order < 0)
    > - order = 0;
    > - if (order >= ARRAY_SIZE(aligns)) {
    > + if (align) {
    > + order = __ffs(align) - 20;
    > + order = (order < 0) ? 0 : order;
    > + }
    > + if (!align || order >= ARRAY_SIZE(aligns)) {
    > pci_warn(dev, "disabling BAR %d: %pR (bad alignment %#llx)\n",
    > i, r, (unsigned long long) align);
    > r->flags = 0;
    >
    >
    Oh I see. Thanks. I'll correct this in v2.

    Thanks,
    Amey

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