linux-kernel - Re: [PATCH v6 1/7] x86/numa: Fix SRAT lookup of CFMWS ranges with numa_fill

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Date: Thu, 2 May 2024 13:59:52 +0200
From: Robert Richter <rrichter@....com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Alison Schofield <alison.schofield@...el.com>,
	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>, Len Brown <lenb@...nel.org>
Subject: Re: [PATCH v6 1/7] x86/numa: Fix SRAT lookup of CFMWS ranges with
 numa_fill_memblks()

On 30.04.24 15:48:56, Jonathan Cameron wrote:
> On Tue, 30 Apr 2024 11:21:54 +0200
> Robert Richter <rrichter@....com> wrote:
> 
> > For configurations that have the kconfig option NUMA_KEEP_MEMINFO
> > disabled numa_fill_memblks() only returns with NUMA_NO_MEMBLK (-1).
> > SRAT lookup fails then because 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.
> > 
> > Fix this by making numa_fill_memblks() always available regardless of
> > NUMA_KEEP_MEMINFO.
> > 
> > The fix also removes numa_fill_memblks() from sparsemem.h using
> > __weak.
> > 
> > From Dan:
> > 
> > """
> > It just feels like numa_fill_memblks() has absolutely no business being
> > defined in arch/x86/include/asm/sparsemem.h.
> > 
> > The only use for numa_fill_memblks() is to arrange for NUMA nodes to be
> > applied to memory ranges hot-onlined by the CXL driver.
> > 
> > It belongs right next to numa_add_memblk(), and I suspect
> > arch/x86/include/asm/sparsemem.h was only chosen to avoid figuring out
> > what to do about the fact that linux/numa.h does not include asm/numa.h
> > and that all implementations either provide numa_add_memblk() or select
> > the generic implementation.
> > 
> > So I would prefer that this do the proper fix and get
> > numa_fill_memblks() completely out of the sparsemem.h path.
> > 
> > Something like the following which boots for me.
> > """
> > 
> > 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, a message is seen then in the logs:
> > 
> >  kernel/numa.c:  pr_info_once("Unknown target node for memory at 0x%llx, assuming node 0\n",
> > 
> > [1] commit fd49f99c1809 ("ACPI: NUMA: Add a node and memblk for each
> >     CFMWS not in SRAT")
> > 
> > Suggested-by: Dan Williams <dan.j.williams@...el.com>
> > Link: https://lore.kernel.org/all/66271b0072317_69102944c@dwillia2-xfh.jf.intel.com.notmuch/
> > 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>
> 
> Whilst I'm not particularly keen on an arch specific solution for this
> and the stub is effectively pointless beyond making the build work, I guess
> this works well enough for now.
> 
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> 
> I was aiming to post the ARM64 handling this cycle but it hasn't quite happened yet :(
> Maybe we can look at whether there is a better level share at than
> the whole function once that is done.

Thanks for review.

It seems better to change x86 to use the generic implementation of
numa_add_memblk() in drivers/base/arch_numa.c. That already contains
code to deal with and merge overlapping blocks, it also checks memory
attributes. But that is not scope of this patch.

-Robert