Re: [Xen-devel] [PATCH v2 02/27] ARM: GICv3: allocate LPI pending and property table

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 21 Mar 2017, André Przywara wrote:
> On 21/03/17 22:57, Stefano Stabellini wrote:
> > On Thu, 16 Mar 2017, Andre Przywara wrote:
> >> The ARM GICv3 provides a new kind of interrupt called LPIs.
> >> The pending bits and the configuration data (priority, enable bits) for
> >> those LPIs are stored in tables in normal memory, which software has to
> >> provide to the hardware.
> >> Allocate the required memory, initialize it and hand it over to each
> >> redistributor. The maximum number of LPIs to be used can be adjusted with
> >> the command line option "max_lpi_bits", which defaults to a compile time
> >> constant exposed in Kconfig.
> >>
> >> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> 
> ....
> 
> >> diff --git a/xen/arch/arm/gic-v3-lpi.c b/xen/arch/arm/gic-v3-lpi.c
> >> new file mode 100644
> >> index 0000000..4f8414b
> >> --- /dev/null
> >> +++ b/xen/arch/arm/gic-v3-lpi.c
> 
> ....
> 
> >> +/*
> >> + * Tell a redistributor about the (shared) property table, allocating one
> >> + * if not already done.
> >> + */
> >> +static int gicv3_lpi_set_proptable(void __iomem * rdist_base)
> >> +{
> >> +    uint64_t reg;
> >> +
> >> +    reg  = GIC_BASER_CACHE_RaWaWb << 
> >> GICR_PROPBASER_INNER_CACHEABILITY_SHIFT;
> >> +    reg |= GIC_BASER_CACHE_SameAsInner << 
> >> GICR_PROPBASER_OUTER_CACHEABILITY_SHIFT;
> >> +    reg |= GIC_BASER_InnerShareable << GICR_PROPBASER_SHAREABILITY_SHIFT;
> >> +
> >> +    /*
> >> +     * The property table is shared across all redistributors, so allocate
> >> +     * this only once, but return the same value on subsequent calls.
> >> +     */
> >> +    if ( !lpi_data.lpi_property )
> >> +    {
> >> +        /* The property table holds one byte per LPI. */
> >> +        unsigned int order = get_order_from_bytes(lpi_data.nr_host_lpis);
> >> +        void *table = alloc_xenheap_pages(order, 0);
> > 
> > you investigated the possibility of using _xmalloc to 64K align it?
> 
> Yes, _xmalloc gives me the alignment, but AFAICT not the physical
> contiguous memory guarantee the table needs. If there are other ways to
> satisfy those requirements, I am all ears. Otherwise I'd just add a
> comment to motivate this.

OK, but the problem is that I am not sure whether alloc_xenheap_pages
makes any guarantees on the alignment of the allocated pages. Is it
possible to allocate 1<<4 pages that are not 64K aligned with it?

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