Re: [PATCH] pstore/ram : Add support for cached pages

[Mukesh Ojha]

On 2/11/2021 1:47 AM, Kees Cook wrote:
> On Wed, Feb 10, 2021 at 08:22:21PM +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.
> Cool; yeah. I like this idea.

Thanks.

> > This commit gives control to change mem_type from Device
> > tree, and also documents the value for normal memory.
> What's the safest default setting?

We could keep it default, like it already exist to have unbuffered or 
not to have it in Device tree.

and could  use mem-type to cover normal memory(DDR)  as cached one and 
it will also cover buffered and unbufferd mapping

by mentioning it in device tree as numeric value.

> > Signed-off-by: Huang Yiwei <hyiwei@xxxxxxxxxxxxxx>
> > Signed-off-by: Mukesh Ojha <mojha@xxxxxxxxxxxxxx>
> > ---
> >   Documentation/admin-guide/ramoops.rst |  4 +++-
> >   fs/pstore/ram.c                       |  1 +
> >   fs/pstore/ram_core.c                  | 10 ++++++++--
> >   3 files changed, 12 insertions(+), 3 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 <sergiu@xxxxxxxxxxxx>
> >   
> > -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..b262c57 100644
> > --- a/fs/pstore/ram.c
> > +++ b/fs/pstore/ram.c
> > @@ -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);
> This was handled by "unbuffered" above. Can you find a way to resolve
> potential conflicts between these?
Currently there is no conflict code-wise, even after this change, as it 
overrides if mem-type is there

otherwise everything is intact.

However, if we want to use only  mem-type property then i can remove 
unbuffered property.

not having unbuffered property i.e default=> mem-type = 0
having unbuffered property => mem-type = 1
mem-type = 2 for cached normal memory

> >   	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..83cd612 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
> It might be nice for this to have a human-readable name too, but let's
> start with numeric. :)
>
> Please update the mem_type MODULE_PARM_DESC to detail the new values too.

Ok, will do in next patch.

> > +
> >   static void *persistent_ram_vmap(phys_addr_t start, size_t size,
> >   		unsigned int memtype)
> >   {
> > @@ -409,9 +413,11 @@ 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)
> > +	if (memtype == MEM_TYPE_NORMAL)
> > +		prot = PAGE_KERNEL;
> > +	else if (memtype == MEM_TYPE_NONCACHED)
> >   		prot = pgprot_noncached(PAGE_KERNEL);
> > -	else
> > +	else if (memtype == MEM_TYPE_WCOMBINE)
> >   		prot = pgprot_writecombine(PAGE_KERNEL);
> Let's make this a switch statement.

Ok, will do in next patch.


Thanks

Mukesh

> >   
> >   	pages = kmalloc_array(page_count, sizeof(struct page *), GFP_KERNEL);
> > --
> > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center,
> > Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project