On Thu, Feb 25, 2021 at 09:30:16PM +0530, Mukesh Ojha wrote:
> There could be a sceanario where we define some region
> in normal memory and use them store to logs which is later
> retrieved by bootloader during warm reset.
>
> In this scenario, we wanted to treat this memory as normal
> cacheable memory instead of default behaviour which
> is an overhead. Making it cacheable could improve
> performance.
>
> This commit gives control to change mem_type from Device
> tree, and also documents the value for normal memory.
>
> Signed-off-by: Mukesh Ojha <[email protected]>
> ---
> Changes in v2:
> - if-else converted to switch case
> - updated MODULE_PARM_DESC with new memory type.
> - default setting is still intact.
>
> Documentation/admin-guide/ramoops.rst | 4 +++-
> fs/pstore/ram.c | 3 ++-
> fs/pstore/ram_core.c | 18 ++++++++++++++++--
> 3 files changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/admin-guide/ramoops.rst
> b/Documentation/admin-guide/ramoops.rst
> index b0a1ae7..8f107d8 100644
> --- a/Documentation/admin-guide/ramoops.rst
> +++ b/Documentation/admin-guide/ramoops.rst
> @@ -3,7 +3,7 @@ Ramoops oops/panic logger
>
> Sergiu Iordache <[email protected]>
>
> -Updated: 17 November 2011
> +Updated: 10 Feb 2021
>
> Introduction
> ------------
> @@ -30,6 +30,8 @@ mapping to pgprot_writecombine. Setting ``mem_type=1``
> attempts to use
> depends on atomic operations. At least on ARM, pgprot_noncached causes the
> memory to be mapped strongly ordered, and atomic operations on strongly
> ordered
> memory are implementation defined, and won't work on many ARMs such as omaps.
> +Setting ``mem_type=2`` attempts to treat the memory region as normal memory,
> +which enables full cache on it. This can improve the performance.
>
> The memory area is divided into ``record_size`` chunks (also rounded down to
> power of two) and each kmesg dump writes a ``record_size`` chunk of
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index ca6d8a8..af4ca6a4 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -56,7 +56,7 @@ MODULE_PARM_DESC(mem_size,
> static unsigned int mem_type;
> module_param(mem_type, uint, 0400);
> MODULE_PARM_DESC(mem_type,
> - "set to 1 to try to use unbuffered memory (default 0)");
> + "set to 1 to use unbuffered memory, 2 for cached memory
> (default 0)");
I'd like to be as explicit as possible (0 wasn't listed), so about this:
"memory type: 0=write-combined (default), 1=unbuffered, 2=cached"
> static int ramoops_max_reason = -1;
> module_param_named(max_reason, ramoops_max_reason, int, 0400);
> @@ -666,6 +666,7 @@ static int ramoops_parse_dt(struct platform_device *pdev,
> field = value; \
> }
>
> + parse_u32("mem-type", pdata->record_size, pdata->mem_type);
Please update the documentation at:
Documentation/devicetree/bindings/reserved-memory/ramoops.txt
(and please move and update the language about "unbuffered" being
deprecated like "no-dump-oops", so that it's clear what happens when
both are specified -- "mem-type" overrides "unbuffered".)
> parse_u32("record-size", pdata->record_size, 0);
> parse_u32("console-size", pdata->console_size, 0);
> parse_u32("ftrace-size", pdata->ftrace_size, 0);
> diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
> index aa8e0b6..0da012f 100644
> --- a/fs/pstore/ram_core.c
> +++ b/fs/pstore/ram_core.c
> @@ -396,6 +396,10 @@ void persistent_ram_zap(struct persistent_ram_zone *prz)
> persistent_ram_update_header_ecc(prz);
> }
>
> +#define MEM_TYPE_WCOMBINE 0
> +#define MEM_TYPE_NONCACHED 1
> +#define MEM_TYPE_NORMAL 2
> +
> static void *persistent_ram_vmap(phys_addr_t start, size_t size,
> unsigned int memtype)
> {
> @@ -409,10 +413,20 @@ static void *persistent_ram_vmap(phys_addr_t start,
> size_t size,
> page_start = start - offset_in_page(start);
> page_count = DIV_ROUND_UP(size + offset_in_page(start), PAGE_SIZE);
>
> - if (memtype)
> + switch (memtype) {
> + case MEM_TYPE_NORMAL:
> + prot = PAGE_KERNEL;
> + break;
> + case MEM_TYPE_NONCACHED:
> prot = pgprot_noncached(PAGE_KERNEL);
> - else
> + break;
> + case MEM_TYPE_WCOMBINE:
> prot = pgprot_writecombine(PAGE_KERNEL);
> + break;
> + default:
> + pr_err("invalid memory type\n");
This should be more verbose:
pr_err("invalid mem_type=%d\n", memtype);
> + return NULL;
> + }
>
> pages = kmalloc_array(page_count, sizeof(struct page *), GFP_KERNEL);
> if (!pages) {
With those changes, it looks good to me. Thanks!
--
Kees Cook
