Hi Pratyush,
On 19/12/16 07:13, Pratyush Anand wrote:
> Purgatory sha verification is very slow when D-cache is not enabled there.
> We need to enable MMU as well to enable D-Cache.Therefore,we need to an
> identity mapped page table in purgatory.
>
> Since debugging is very difficult in purgatory therefore we prefer to do as
> much work as possible in kexec.
>
> This patch prepares page table for purgatory in advance. We support only 4K
> page table,because it will be available on most of the platform. This page
> table is passed to the purgatory as a new segment.
>
> VA bit is fixed as 48, page table level is 3 where 3rd level page table
> contains 2M block entries.
> diff --git a/kexec/arch/arm64/kexec-arm64.c b/kexec/arch/arm64/kexec-arm64.c
> index 04fd3968bb52..c2c8ff1b6940 100644
> --- a/kexec/arch/arm64/kexec-arm64.c
> +++ b/kexec/arch/arm64/kexec-arm64.c
> @@ -24,6 +24,45 @@
> #include "kexec-syscall.h"
> #include "arch/options.h"
>
> +/*
> + * kexec creates identity page table to be used in purgatory so that
> + * dcache verification becomes faster.
> + *
> + * These are the definitions to be used by page table creation routine.
> + *
> + * Only 4K page table, 3 level, 2M block mapping, 48bit VA is supported
> + */
> +#define PGDIR_SHIFT 39
> +#define PUD_SHIFT 30
> +#define PMD_SHIFT 21
> +#define PTRS_PER_PGD 0x1FF
> +#define PTRS_PER_PUD 0x1FF
> +#define PTRS_PER_PMD 0x1FF
Aren't these 0x200 for 4K pages in the kernel? It looks like you use them as a
mask instead.
> +#define PMD_TYPE_TABLE (3UL << 0)
> +#define PMD_TYPE_SECT (1UL << 0)
> +#define PMD_SECT_AF (1UL << 10)
> +#define PMD_ATTRINDX(t) ((unsigned long)(t) << 2)
> +#define MT_NORMAL 4
This needs to correspond to the part of MAIR that describes the memory type for
'normal'. You define MT_NORMAL again in the next patch, it would be better to
share the definition so they can't be different. (I don't see why you can't use
0!)
> +#define PMD_FLAGS_NORMAL (PMD_TYPE_SECT | PMD_SECT_AF)
> +#define MMU_FLAGS_NORMAL (PMD_ATTRINDX(MT_NORMAL) | PMD_FLAGS_NORMAL)
The SH and AP bits are left as zero, which means non-shareable, read/writeable,
(which I think is fine).
> +#define SECTION_SIZE (2 * 1024 * 1024)
> +#define PAGE_SIZE (4 * 1024)
> +/* Since we are using 3 level of page tables, therefore minimum number of
> + * table will be 3. Most likely we will never need more than 3. Each entry
> + * in level 3 page table can map 2MB memory area. Thus a level 3 page table
> + * indexed by bit 29:21 can map a total of 1G memory area. Therefore, if
> + * any segment crosses 1G boundary, then we will need one more level 3
> + * table. Similarly, level 2 page table indexed by bit 38:30 can map a
> + * total of 512G memory area. If segment addresses are more than 512G apart
> + * then we will need two more table for each such block. We do not expect
> + * any memory segment to cross 512G boundary, however if we will ever wish
> + * to support uart debugging in purgatory then that might cross the
> + * boundary and therefore additional 2 more table space. Thus we will need
> + * maximum of 6 table space.
Surely we only need 6 page_size table entries if we support uart debugging,
which your 'if we ever' suggests we don't. So surely we only need 3, and a
comment that this needs expanding to 6 if we need to map two distinct areas.
> + */
> +#define MAX_PGTBLE_SZ (6 * 4096)
> +static int next_tbl_cnt = 1;
> +
> /* Global varables the core kexec routines expect. */
>
> unsigned char reuse_initrd;
> @@ -316,6 +355,117 @@ unsigned long arm64_locate_kernel_segment(struct
> kexec_info *info)
> return hole;
> }
>
> +static unsigned long *create_table_entry(unsigned long *pgtbl_buf,
> + unsigned long pgtbl_mem, unsigned long *tbl,
> + unsigned long virt, int shift,
> + unsigned long ptrs)
> +{
> + unsigned long index, desc, offset;
> +
> + index = (virt >> shift) & ptrs;
> + /* check if we have allocated a table already for this index */
> + if (tbl[index]) {
> + /*
> + * table index will have entry as per purgatory page table
> + * memory. Find out corresponding buffer address of table.
> + */
> + desc = tbl[index] & ~3UL;
> + offset = desc - pgtbl_mem;
wait .. no .. pgtbl_mem is also a guest physical address, so this is fine... its
not obvious at first glance! You could do with a typedef to make it clear which
addresses are the guests (pgtable_mem) and which are the hosts (pgtable_buf).
Something like phys_addr_t?
> + return &pgtbl_buf[offset >> 3];
> + }
> +
> + /*
> + * Always write page table content as per page table memory allocated
> + * for purgaory area, but return corresponding buffer area alloced
Nit: purgatory, allocated,
> + * in kexec
> + */
> + if (next_tbl_cnt > 5)
> + die("%s: No more memory for page table\n", __func__);
die()? With a bit of juggling can't we return an error so we never try to enable
the MMU+dcache instead?
> +
> + tbl[index] = (pgtbl_mem + PAGE_SIZE * next_tbl_cnt) | PMD_TYPE_TABLE;
> +
> + return &pgtbl_buf[(next_tbl_cnt++ * PAGE_SIZE) >> 3];
> +}
> +
> +static void craete_block_entry(unsigned long *tbl, unsigned long flags,
> + unsigned long phys, unsigned long virt)
Why have separate phys and virt parameters if all this ever does is idmap?
> +{
> + unsigned long index;
> + unsigned long desc;
> +
> + index = (virt >> PMD_SHIFT) & PTRS_PER_PMD;
Copying the pmd_index() macro would make this clearer.
> + desc = (phys >> PMD_SHIFT) << PMD_SHIFT;
Looks like you wanted a PMD_MASK.
> + desc |= flags;
> + tbl[index] = desc;
> +}
> +
> +static void create_identity_entry(unsigned long *pgtbl_buf,
> + unsigned long pgtbl_mem, unsigned long virt,
> + unsigned long flags)
> +{
> + unsigned long *tbl = pgtbl_buf;
> +
> + tbl = create_table_entry(pgtbl_buf, pgtbl_mem, tbl, virt,
> + PGDIR_SHIFT, PTRS_PER_PGD);
> + tbl = create_table_entry(pgtbl_buf, pgtbl_mem, tbl, virt,
> + PUD_SHIFT, PTRS_PER_PUD);
> + craete_block_entry(tbl, flags, virt, virt);
Nit: create
> +}
> +
> +/**
> + * arm64_create_pgtbl_segment - Create page table segments to be used by
> + * purgatory. Page table will have entries to access memory area of all
> + * those segments which becomes part of sha verification in purgatory.
> + * Additionaly, we also create page table for purgatory segment as well.
Nit: additionally,
> + */
> +
> +static int arm64_create_pgtbl_segment(struct kexec_info *info,
> + unsigned long hole_min, unsigned long hole_max)
> +{
> + unsigned long *pgtbl_buf;
> + int i;
> + unsigned long mstart, mend, pgtbl_mem;
> + unsigned long purgatory_base, purgatory_len;
> +
> + pgtbl_buf = xmalloc(MAX_PGTBLE_SZ);
> + memset(pgtbl_buf, 0, MAX_PGTBLE_SZ);
> + pgtbl_mem = add_buffer_phys_virt(info, pgtbl_buf, MAX_PGTBLE_SZ,
> + MAX_PGTBLE_SZ, PAGE_SIZE, hole_min, hole_max, 1, 0);
I want to check what this does, but this all looks like it is doing the right
thing.
> + for (i = 0; i < info->nr_segments; i++) {
> + if (info->segment[i].mem == (void *)info->rhdr.rel_addr) {
> + purgatory_base = (unsigned long)info->segment[i].mem;
> + purgatory_len = info->segment[i].memsz;
> + }
> + mstart = (unsigned long)info->segment[i].mem;
> + mend = mstart + info->segment[i].memsz;
> + mstart &= ~(SECTION_SIZE - 1);
> + while (mstart < mend) {
> + create_identity_entry(pgtbl_buf, pgtbl_mem,
> + mstart, MMU_FLAGS_NORMAL);
> + mstart += SECTION_SIZE;
> + }
> + }
Thanks,
James
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