Re: [PATCH 1/2] arm64: account for GICv3 LPI tables in static memblock reserve table

Ard Biesheuvel
2019-02-14T16:55:46Z

On Thu, 14 Feb 2019 at 16:48, Marc Zyngier <marc.zyngier@arm.com> wrote:
>
> Hi Ard,
>
> On 13/02/2019 13:27, Ard Biesheuvel wrote:
> > In the irqchip and EFI code, we have what basically amounts to a quirk
> > to work around a peculiarity in the GICv3 architecture, which permits
> > the system memory address of LPI tables to be programmable only once
> > after a CPU reset. This means kexec kernels must use the same memory
> > as the first kernel, and thus ensure that this memory has not been
> > given out for other purposes by the time the ITS init code runs, which
> > is not very early for secondary CPUs.
> >
> > On systems with many CPUs, these reservations could overflow the
> > memblock reservation table, and this was addressed in commit
> > eff896288872 ("efi/arm: Defer persistent reservations until after
> > paging_init()"). However, this turns out to have made things worse,
> > since the allocation of page tables and heap space for the resized
> > memblock reservation table itself may overwrite the regions we are
> > attempting to reserve, which may cause all kinds of corruption,
> > also considering that the ITS will still be poking bits into that
> > memory in response to incoming MSIs.
> >
> > So instead, let's grow the static memblock reservation table on such
> > systems so it can accommodate these reservations at an earlier time.
> > This will permit us to revert the above commit in a subsequent patch.
> >
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > ---
> > arch/arm64/include/asm/memory.h | 11 +++++++++++
> > include/linux/memblock.h | 3 ---
> > mm/memblock.c | 10 ++++++++--
> > 3 files changed, 19 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> > index e1ec947e7c0c..7e2b13cdd970 100644
> > --- a/arch/arm64/include/asm/memory.h
> > +++ b/arch/arm64/include/asm/memory.h
> > @@ -332,6 +332,17 @@ static inline void *phys_to_virt(phys_addr_t x)
> > #define virt_addr_valid(kaddr) \
> > (_virt_addr_is_linear(kaddr) && _virt_addr_valid(kaddr))
> >
> > +/*
> > + * Given that the GIC architecture permits ITS implementations that can only be
> > + * configured with a LPI table address once, GICv3 systems with many CPUs may
> > + * end up reserving a lot of different regions after a kexec for their LPI
> > + * tables, as we are forced to reuse the same memory after kexec (and thus
> > + * reserve it persistently with EFI beforehand)
> > + */
> > +#if defined(CONFIG_EFI) && defined(CONFIG_ARM_GIC_V3_ITS)
> > +#define INIT_MEMBLOCK_RESERVED_REGIONS (INIT_MEMBLOCK_REGIONS + 2 * NR_CPUS)
>
> Since GICv3 has 1 pending table per CPU, plus one global property table,
> can we make this 2 * NR_CPUS + 1? Or is that enough already?
>

Ah, I misread the code then. That would mean we'll only need 1 extra
slot per CPU.

So I will change this to

> > +#define INIT_MEMBLOCK_RESERVED_REGIONS (INIT_MEMBLOCK_REGIONS + NR_CPUS)

considering that INIT_MEMBLOCK_REGIONS defaults to 128, so that one
global table is already accounted for.

> > +#endif
> > +
> > #include <asm-generic/memory_model.h>
> >
> > #endif
> > diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> > index 64c41cf45590..859b55b66db2 100644
> > --- a/include/linux/memblock.h
> > +++ b/include/linux/memblock.h
> > @@ -29,9 +29,6 @@ extern unsigned long max_pfn;
> > */
> > extern unsigned long long max_possible_pfn;
> >
> > -#define INIT_MEMBLOCK_REGIONS 128
> > -#define INIT_PHYSMEM_REGIONS 4
> > -
> > /**
> > * enum memblock_flags - definition of memory region attributes
> > * @MEMBLOCK_NONE: no special request
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index 022d4cbb3618..a526c3ab8390 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -26,6 +26,12 @@
> >
> > #include "internal.h"
> >
> > +#define INIT_MEMBLOCK_REGIONS 128
> > +#define INIT_PHYSMEM_REGIONS 4
> > +#ifndef INIT_MEMBLOCK_RESERVED_REGIONS
> > +#define INIT_MEMBLOCK_RESERVED_REGIONS INIT_MEMBLOCK_REGIONS
> > +#endif
> > +
> > /**
> > * DOC: memblock overview
> > *
> > @@ -92,7 +98,7 @@ unsigned long max_pfn;
> > unsigned long long max_possible_pfn;
> >
> > static struct memblock_region memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS] __initdata_memblock;
> > -static struct memblock_region memblock_reserved_init_regions[INIT_MEMBLOCK_REGIONS] __initdata_memblock;
> > +static struct memblock_region memblock_reserved_init_regions[INIT_MEMBLOCK_RESERVED_REGIONS] __initdata_memblock;
> > #ifdef CONFIG_HAVE_MEMBLOCK_PHYS_MAP
> > static struct memblock_region memblock_physmem_init_regions[INIT_PHYSMEM_REGIONS] __initdata_memblock;
> > #endif
> > @@ -105,7 +111,7 @@ struct memblock memblock __initdata_memblock = {
> >
> > .reserved.regions = memblock_reserved_init_regions,
> > .reserved.cnt = 1, /* empty dummy entry */
> > - .reserved.max = INIT_MEMBLOCK_REGIONS,
> > + .reserved.max = INIT_MEMBLOCK_RESERVED_REGIONS,
> > .reserved.name = "reserved",
> >
> > #ifdef CONFIG_HAVE_MEMBLOCK_PHYS_MAP
> >
>
> Otherwise:
>
> Acked-by: Marc Zyngier <marc.zyngier@arm.com>
>
> M.
> --
> Jazz is not dead. It just smells funny...