Messages in this thread | | | From | Ard Biesheuvel <> | Date | Tue, 18 Apr 2023 12:06:49 +0200 | Subject | Re: [PATCH v3 34/60] arm64: head: Move early kernel mapping routines into C code |
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On Tue, 18 Apr 2023 at 11:31, Ryan Roberts <ryan.roberts@arm.com> wrote: > > On 07/03/2023 14:04, Ard Biesheuvel wrote: > > The asm version of the kernel mapping code works fine for creating a > > coarse grained identity map, but for mapping the kernel down to its > > exact boundaries with the right attributes, it is not suitable. This is > > why we create a preliminary RWX kernel mapping first, and then rebuild > > it from scratch later on. > > > > So let's reimplement this in C, in a way that will make it unnecessary > > to create the kernel page tables yet another time in paging_init(). > > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > > --- > > > [...] > > > diff --git a/arch/arm64/kernel/pi/map_kernel.c b/arch/arm64/kernel/pi/map_kernel.c > > new file mode 100644 > > index 0000000000000000..b573c964c7d88d1b > > --- /dev/null > > +++ b/arch/arm64/kernel/pi/map_kernel.c > > @@ -0,0 +1,171 @@ > > +// SPDX-License-Identifier: GPL-2.0-only > > +// Copyright 2023 Google LLC > > +// Author: Ard Biesheuvel <ardb@google.com> > > + > > +#include <linux/init.h> > > +#include <linux/libfdt.h> > > +#include <linux/linkage.h> > > +#include <linux/types.h> > > +#include <linux/sizes.h> > > +#include <linux/string.h> > > + > > +#include <asm/memory.h> > > +#include <asm/pgalloc.h> > > +#include <asm/pgtable.h> > > +#include <asm/tlbflush.h> > > + > > +#include "pi.h" > > + > > +extern const u8 __eh_frame_start[], __eh_frame_end[]; > > + > > +extern void idmap_cpu_replace_ttbr1(void *pgdir); > > + > > +static void map_segment(pgd_t *pg_dir, u64 *pgd, u64 va_offset, > > + void *start, void *end, pgprot_t prot, > > + bool may_use_cont, int root_level) > > +{ > > + map_range(pgd, ((u64)start + va_offset) & ~PAGE_OFFSET, > > + ((u64)end + va_offset) & ~PAGE_OFFSET, (u64)start, > > + prot, root_level, (pte_t *)pg_dir, may_use_cont, 0); > > I don't understand what you are doing with ~PAGE_OFFSET here. Is this intended > to be page alignment with PAGE_MASK? I'm guessing not, because you would want to > forward align the end address in that case. >
start + va_offset will produce an address that has leading 1 bits set in positions that do not contribute to the translation. In order to index the page tables correctly, those bits need to be cleared.
> > +} > > + > > +static void unmap_segment(pgd_t *pg_dir, u64 va_offset, void *start, > > + void *end, int root_level) > > +{ > > + map_segment(pg_dir, NULL, va_offset, start, end, __pgprot(0), > > + false, root_level); > > +} > > + > > > [...] > > > diff --git a/arch/arm64/kernel/pi/map_range.c b/arch/arm64/kernel/pi/map_range.c > > new file mode 100644 > > index 0000000000000000..61cbd6e82418c033 > > --- /dev/null > > +++ b/arch/arm64/kernel/pi/map_range.c > > @@ -0,0 +1,87 @@ > > +// SPDX-License-Identifier: GPL-2.0-only > > +// Copyright 2023 Google LLC > > +// Author: Ard Biesheuvel <ardb@google.com> > > + > > +#include <linux/types.h> > > +#include <linux/sizes.h> > > + > > +#include <asm/memory.h> > > +#include <asm/pgalloc.h> > > +#include <asm/pgtable.h> > > + > > +#include "pi.h" > > + > > +/** > > + * map_range - Map a contiguous range of physical pages into virtual memory > > + * > > + * @pte: Address of physical pointer to array of pages to > > + * allocate page tables from > > + * @start: Virtual address of the start of the range > > + * @end: Virtual address of the end of the range (exclusive) > > + * @pa: Physical address of the start of the range > > + * @level: Translation level for the mapping > > + * @tbl: The level @level page table to create the mappings in > > + * @may_use_cont: Whether the use of the contiguous attribute is allowed > > + * @va_offset: Offset between a physical page and its current mapping > > + * in the VA space > > + */ > > +void __init map_range(u64 *pte, u64 start, u64 end, u64 pa, pgprot_t prot, > > + int level, pte_t *tbl, bool may_use_cont, u64 va_offset) > > va_offset is always 0 (because the memory at *pte is id-mapped). Can it be > dropped? Or perhaps you are using this function later, once the memory is no > longer id-mapped? >
It will be used later.
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