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

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Date: Wed, 20 Mar 2024 10:46:07 -0700
From: Alison Schofield <alison.schofield@...el.com>
To: Robert Richter <rrichter@....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()

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;
+       }
+
        /* 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
>