On Wed, Aug 02, 2023 at 11:48:18AM -0400, Stefan Berger wrote:
> When a kernel dump is present then restrict the high memory regions to
> avoid allocating memory where the kernel dump resides. Use the
> ibm,kernel-dump node under /rtas to determine whether a kernel dump exists
> and up to which limit grub can use available memory. Set the
> upper_mem_limit to the size of the kernel dump section of type
> 'REAL_MODE_REGION' and therefore only allow grub's memory usage for high
> addresses from RMO_ADDR_MAX to 'upper_mem_limit'. This means that grub can
> use high memory in the range of RMO_ADDR_MAX (768MB) to upper_mem_limit and
> the kernel-dump memory regions above 'upper_mem_limit' remain untouched.
> This change has no effect on memory allocations below 'linux_rmo_save'
> (typically at 640MB).
>
> Also, fall back to allocating below rmo_linux_save in case the chunk of
> memory there would be larger than the chunk of memory above RMO_ADDR_MAX.
> This can for example occur if a free memory area is found starting at 300MB
> extending up to 1GB but a kernel dump is located at 768MB and therefore
> does not allow the allocation of the high memory area but requiring to use
> the chunk starting at 300MB to avoid an unnecessary out-of-memory
> condition.
>
> Signed-off-by: Stefan Berger <stef...@linux.ibm.com>
> Reviewed-by: Hari Bathini <hbath...@linux.ibm.com>
> Cc: Pavithra Prakash <pavra...@in.ibm.com>
> Cc: Michael Ellerman <m...@ellerman.id.au>
> Cc: Carolyn Scherrer <cpsch...@us.ibm.com>
> Cc: Mahesh Salgaonkar <mah...@linux.ibm.com>
> Cc: Sourabh Jain <sourabhj...@linux.ibm.com>
> ---
> grub-core/kern/ieee1275/init.c | 145 ++++++++++++++++++++++++++++++++-
> 1 file changed, 143 insertions(+), 2 deletions(-)
>
> diff --git a/grub-core/kern/ieee1275/init.c b/grub-core/kern/ieee1275/init.c
> index bd9a4804b..ed609070a 100644
> --- a/grub-core/kern/ieee1275/init.c
> +++ b/grub-core/kern/ieee1275/init.c
> @@ -17,6 +17,8 @@
> * along with GRUB. If not, see <http://www.gnu.org/licenses/>.
> */
>
> +#include <stddef.h> /* offsetof() */
> +
> #include <grub/kernel.h>
> #include <grub/dl.h>
> #include <grub/disk.h>
> @@ -196,6 +198,96 @@ grub_claim_heap (void)
> #else
> /* Helpers for mm on powerpc. */
>
> +/* ibm,kernel-dump data structures */
> +struct kd_section
> +{
> + grub_uint32_t flags;
> + grub_uint16_t src_datatype;
> +#define KD_SRC_DATATYPE_REAL_MODE_REGION 0x0011
> + grub_uint16_t error_flags;
> + grub_uint64_t src_address;
> + grub_uint64_t num_bytes;
> + grub_uint64_t act_bytes;
> + grub_uint64_t dst_address;
> +} GRUB_PACKED;
> +
> +#define MAX_KD_SECTIONS 10
> +
> +struct kernel_dump
> +{
> + grub_uint32_t format;
> + grub_uint16_t num_sections;
> + grub_uint16_t status_flags;
> + grub_uint32_t offset_1st_section;
> + grub_uint32_t num_blocks;
> + grub_uint64_t start_block;
> + grub_uint64_t num_blocks_avail;
> + grub_uint32_t offet_path_string;
> + grub_uint32_t max_time_allowed;
> + struct kd_section kds[MAX_KD_SECTIONS]; /* offset_1st_section should point
> to kds[0] */
> +} GRUB_PACKED;
> +
> +/*
> + * Determine if a kernel dump exists and if it does, then determine the
> highest
> + * address that grub can use for memory allocations.
> + * The caller must have initialized *highest to rmo_top. *highest will not
> + * be modified if no kernel dump is found.
> + */
> +static int
> +check_kernel_dump (grub_uint64_t *highest)
> +{
> + struct kernel_dump kernel_dump;
> + grub_ssize_t kernel_dump_size;
> + grub_ieee1275_phandle_t rtas;
> + struct kd_section *kds;
> + grub_size_t i;
> +
> + /* If there's a kernel-dump it must have at least one section */
> + if (grub_ieee1275_finddevice ("/rtas", &rtas) ||
> + grub_ieee1275_get_property (rtas, "ibm,kernel-dump", &kernel_dump,
> + sizeof (kernel_dump), &kernel_dump_size) ||
> + kernel_dump_size <= (grub_ssize_t) offsetof (struct kernel_dump,
> kds[1]))
> + return 0;
> +
> + kernel_dump_size = grub_min (kernel_dump_size, (grub_ssize_t) sizeof
> (kernel_dump));
> +
> + if (grub_be_to_cpu32 (kernel_dump.format) != 1)
> + {
> + grub_printf (_("Error: ibm,kernel-dump has an unexpected format
> version '%u'\n"),
> + grub_be_to_cpu32 (kernel_dump.format));
> + return 0;
> + }
> +
> + if (grub_be_to_cpu16 (kernel_dump.num_sections) > MAX_KD_SECTIONS)
> + {
> + grub_printf (_("Error: Too many kernel dump sections: %d\n"),
> + grub_be_to_cpu32 (kernel_dump.num_sections));
> + return 0;
> + }
> +
> + for (i = 0; i < grub_be_to_cpu16 (kernel_dump.num_sections); i++)
> + {
> + kds = (struct kd_section *) ((grub_addr_t) &kernel_dump +
> + grub_be_to_cpu32
> (kernel_dump.offset_1st_section) +
> + i * sizeof (struct kd_section));
> + /* sanity check the address is within the 'kernel_dump' struct */
> + if ((grub_addr_t) kds > (grub_addr_t) &kernel_dump + kernel_dump_size
> + sizeof (*kds))
> + {
> + grub_printf (_("Error: 'kds' address beyond last available
> section\n"));
> + return 0;
> + }
> +
> + if ((grub_be_to_cpu16 (kds->src_datatype) ==
> KD_SRC_DATATYPE_REAL_MODE_REGION) &&
> + (grub_be_to_cpu64 (kds->src_address) == 0))
> + {
> + *highest = grub_min (*highest, grub_be_to_cpu64 (kds->num_bytes));
> + break;
> + }
> + }
> +
> + return 1;
> +}
> +
> /*
> * How much memory does OF believe exists in total?
> *
> @@ -275,10 +367,31 @@ regions_claim (grub_uint64_t addr, grub_uint64_t len,
> grub_memory_type_t type,
> *
> * Finally, we also want to make sure that when grub loads the kernel,
> * it isn't going to use up all the memory we're trying to reserve! So
> - * enforce our entire RUNTIME_MIN_SPACE here:
> + * enforce our entire RUNTIME_MIN_SPACE here (no fadump):
> + *
> + * | Top of memory == upper_mem_limit -|
> + * | |
> + * | available |
> + * | |
> + * |---------- 768 MB ----------|
> + * | |
> + * | reserved |
> + * | |
> + * |--- 768 MB - runtime min space ---|
> + * | |
> + * | available |
> + * | |
> + * |---------- 0 MB ----------|
> + *
> + * In case fadump is used, we allow the following:
> *
> * |---------- Top of memory ----------|
> * | |
> + * | unavailable |
> + * | (kernel dump area) |
> + * | |
> + * |--------- upper_mem_limit ---------|
> + * | |
> * | available |
> * | |
> * |---------- 768 MB ----------|
> @@ -333,17 +446,45 @@ regions_claim (grub_uint64_t addr, grub_uint64_t len,
> grub_memory_type_t type,
> }
> else
> {
> + grub_uint64_t upper_mem_limit = rmo_top;
> + grub_uint64_t orig_addr = addr;
> + int has_kernel_dump;
> +
> + has_kernel_dump = check_kernel_dump (&upper_mem_limit);
Compiler complains... :-(
kern/ieee1275/init.c: In function ‘regions_claim’:
kern/ieee1275/init.c:451:15: error: variable ‘has_kernel_dump’ set but not used
[-Werror=unused-but-set-variable]
int has_kernel_dump;
^~~~~~~~~~~~~~~
If you do not use check_kernel_dump() return value than maybe you
should return void. Should not you?
Daniel
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