linux-kernel - Re: [PATCH v2 1/3] x86/numa: Fix SRAT lookup of CFMWS ranges with numa_fill

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Date: Thu, 21 Mar 2024 17:55:57 +0100
From: Robert Richter <rrichter@....com>
To: Alison Schofield <alison.schofield@...el.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	x86@...nel.org, Dan Williams <dan.j.williams@...el.com>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-cxl@...r.kernel.org, Derick Marks <derick.w.marks@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 1/3] x86/numa: Fix SRAT lookup of CFMWS ranges with
 numa_fill_memblks()

Alison,

On 20.03.24 10:46:07, Alison Schofield wrote:
> On Tue, Mar 19, 2024 at 01:00:23PM +0100, Robert Richter wrote:
> > For configurations that have the kconfig option NUMA_KEEP_MEMINFO
> > disabled, the SRAT lookup done with numa_fill_memblks() fails
> > returning NUMA_NO_MEMBLK (-1). An existing SRAT memory range cannot be
> > found for a CFMWS address range. This causes the addition of a
> > duplicate numa_memblk with a different node id and a subsequent page
> > fault and kernel crash during boot.
> > 
> > numa_fill_memblks() is implemented and used in the init section only.
> > The option NUMA_KEEP_MEMINFO is only for the case when NUMA data will
> > be used outside of init. So fix the SRAT lookup by moving
> > numa_fill_memblks() out of the NUMA_KEEP_MEMINFO block to make it
> > always available in the init section.
> > 
> > Note that the issue was initially introduced with [1]. But since
> > phys_to_target_node() was originally used that returned the valid node
> > 0, an additional numa_memblk was not added. Though, the node id was
> > wrong too.
> 
> Hi Richard,
> 
> I recall a bit of wrangling w #defines to make ARM64 and LOONGARCH build.
> I'm seeing an x86 build error today:
> 
> >> arch/x86/mm/numa.c:957:12: error: redefinition of 'numa_fill_memblks'
>      957 | int __init numa_fill_memblks(u64 start, u64 end)
> 
> include/linux/numa.h:40:26: note: previous definition of 'numa_fill_memblks' with type
> +'int(u64,  u64)' {aka 'int(long long unsigned int,  long long unsigned int)'}
>       40 | static inline int __init numa_fill_memblks(u64 start, u64 end)
>          |                          ^~~~~~~~~~~~~~~~~
> 
> In addition to what you suggest, would something like this diff below be
> a useful safety measure to distinguish num_fill_memblks() success (rc:0)
> and possible non-existence (rc:-1). I don't think it hurts to take a
> second look using phys_to_target_node() (totall untested)
> 
> diff --git a/drivers/acpi/numa/srat.c b/drivers/acpi/numa/srat.c
> index 070a52e4daa8..0c48fe32ced4 100644
> --- a/drivers/acpi/numa/srat.c
> +++ b/drivers/acpi/numa/srat.c
> @@ -437,9 +437,16 @@ static int __init acpi_parse_cfmws(union acpi_subtable_headers *header,
>          * found for any portion of the window to cover the entire
>          * window.
>          */
> -       if (!numa_fill_memblks(start, end))
> +       rc = numa_fill_memblks(start, end);
> +       if (!rc)
>                 return 0;
>  
> +       if (rc == NUMA_NO_MEMBLK) {
> +               node = phys_to_target_node(start);
> +               if (node != NUMA_NO_NODE)
> +                       return 0;
> +       }
> +

for non-x86 the numa_add_memblk() function looks good in a way that it
is able to handle presumable overlapping regions. numa_fill_memblks()
would just fail then and numa_add_memblk() being called. For x86 we
need numa_fill_memblks() since x86 specific numa_add_memblk() cannot
handle the overlapping case.

That said, we do not need the 2nd check. It looks to me that it
actually breaks non-x86 as the whole block may not be registered (if
it is larger than anything existing).

For x86 the 2nd check may never happen if numa_fill_memblks() is
always enabled (which is this patch for).

So we should be good without your change.

Thanks,

-Robert

>         /* No SRAT description. Create a new node. */
> 
> --Alison
> 
> > 
> > [1] fd49f99c1809 ("ACPI: NUMA: Add a node and memblk for each CFMWS not in SRAT")
> > 
> > Fixes: 8f1004679987 ("ACPI/NUMA: Apply SRAT proximity domain to entire CFMWS window")
> > Cc: Derick Marks <derick.w.marks@...el.com>
> > Cc: Dan Williams <dan.j.williams@...el.com>
> > Cc: Alison Schofield <alison.schofield@...el.com>
> > Signed-off-by: Robert Richter <rrichter@....com>
> > ---
> >  arch/x86/mm/numa.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> > index 65e9a6e391c0..ce84ba86e69e 100644
> > --- a/arch/x86/mm/numa.c
> > +++ b/arch/x86/mm/numa.c
> > @@ -929,6 +929,8 @@ int memory_add_physaddr_to_nid(u64 start)
> >  }
> >  EXPORT_SYMBOL_GPL(memory_add_physaddr_to_nid);
> >  
> > +#endif
> > +
> >  static int __init cmp_memblk(const void *a, const void *b)
> >  {
> >  	const struct numa_memblk *ma = *(const struct numa_memblk **)a;
> > @@ -1001,5 +1003,3 @@ int __init numa_fill_memblks(u64 start, u64 end)
> >  	}
> >  	return 0;
> >  }
> > -
> > -#endif
> > -- 
> > 2.39.2
> >