[PATCH v6 04/41] arm64: mm: Move PCI I/O emulation region above the vmemmap region

[Ard Biesheuvel]

On Thu, 30 Nov 2023 at 09:52, Anshuman Khandual
<anshuman.khandual at arm.com> wrote:
>
>
>
> On 11/30/23 13:32, Ard Biesheuvel wrote:
> > On Thu, 30 Nov 2023 at 08:59, Anshuman Khandual
> > <anshuman.khandual at arm.com> wrote:
> >>
> >>
> >>
> >> On 11/29/23 16:46, Ard Biesheuvel wrote:
> >>> From: Ard Biesheuvel <ardb at kernel.org>
> >>>
> >>> Move the PCI I/O region above the vmemmap region in the kernel's VA
> >>> space. This will permit us to reclaim the lower part of the vmemmap
> >>> region for vmalloc/vmap allocations when running a 52-bit VA capable
> >>> build on a 48-bit VA capable system.
> >>>
> >>> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> >>> ---
> >>>  arch/arm64/include/asm/memory.h | 4 ++--
> >>>  arch/arm64/mm/ptdump.c          | 4 ++--
> >>>  2 files changed, 4 insertions(+), 4 deletions(-)
> >>>
> >>> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> >>> index b8d726f951ae..99caeff78e1a 100644
> >>> --- a/arch/arm64/include/asm/memory.h
> >>> +++ b/arch/arm64/include/asm/memory.h
> >>> @@ -49,8 +49,8 @@
> >>>  #define MODULES_VSIZE                (SZ_2G)
> >>>  #define VMEMMAP_START                (-(UL(1) << (VA_BITS - VMEMMAP_SHIFT)))
> >>>  #define VMEMMAP_END          (VMEMMAP_START + VMEMMAP_SIZE)
> >>> -#define PCI_IO_END           (VMEMMAP_START - SZ_8M)
> >>> -#define PCI_IO_START         (PCI_IO_END - PCI_IO_SIZE)
> >>> +#define PCI_IO_START         (VMEMMAP_END + SZ_8M)
> >>> +#define PCI_IO_END           (PCI_IO_START + PCI_IO_SIZE)
> >>>  #define FIXADDR_TOP          (VMEMMAP_START - SZ_32M)
> >>>
> >>>  #if VA_BITS > 48
> >>> diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
> >>> index e305b6593c4e..d1df56d44f8a 100644
> >>> --- a/arch/arm64/mm/ptdump.c
> >>> +++ b/arch/arm64/mm/ptdump.c
> >>> @@ -47,10 +47,10 @@ static struct addr_marker address_markers[] = {
> >>>       { VMALLOC_END,                  "vmalloc() end" },
> >>>       { FIXADDR_TOT_START,            "Fixmap start" },
> >>>       { FIXADDR_TOP,                  "Fixmap end" },
> >>> -     { PCI_IO_START,                 "PCI I/O start" },
> >>> -     { PCI_IO_END,                   "PCI I/O end" },
> >>>       { VMEMMAP_START,                "vmemmap start" },
> >>>       { VMEMMAP_START + VMEMMAP_SIZE, "vmemmap end" },
> >>> +     { PCI_IO_START,                 "PCI I/O start" },
> >>> +     { PCI_IO_END,                   "PCI I/O end" },
> >>>       { -1,                           NULL },
> >>>  };
> >>>
> >
> > Hi Anshuman,
> >
> >>
> >> I have not debugged this any further, but the PCI region displays no entries
> >> via ptdump just after this patch being applied.
> >>
> >
> > It also does not display any mappings without the patch. What exactly
> > were you expecting to see here?
>
> Is not there a single entry inside - without this patch section. OR does
> it signify the gap-width of the PCI mapping area ?
>
> ---[ PCI I/O start ]---
> 0xfffffbfffe800000-0xfffffbffff800000          16M PMD
> ---[ PCI I/O end ]---
>

This means that the PCI I/O space is covered by 8 invalid level 2 entries.


> >> 0xfffffe0000000000-0xfffffe8000000000         512G PGD
> >> ---[ PCI I/O start ]---
> >> ---[ PCI I/O end ]---                                   -----> No entries
> >> 0xfffffe8000000000-0x0000000000000000        1536G PGD

This means that the PCI I/O space is covered by 1 invalid level 0 entry.