linux-kernel - Re: [PATCH v6 13/14] arm64, acpi, numa: NUMA support based on SRAT and SLIT

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Date:	Thu, 12 May 2016 17:24:49 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Will Deacon <will.deacon@....com>,
	Mark Rutland <mark.rutland@....com>,
	linux-ia64@...r.kernel.org, David Daney <david.daney@...ium.com>,
	Robert Moore <robert.moore@...el.com>,
	Lv Zheng <lv.zheng@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frank Rowand <frowand.list@...il.com>, x86@...nel.org,
	linux-acpi@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Grant Likely <grant.likely@...aro.org>,
	Len Brown <lenb@...nel.org>, Fenghua Yu <fenghua.yu@...el.com>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Jon Masters <jcm@...hat.com>,
	Robert Richter <rrichter@...ium.com>,
	Rob Herring <robh+dt@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-arm-kernel@...ts.infradead.org, devel@...ica.org,
	Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Ganapatrao Kulkarni <gkulkarni@...iumnetworks.com>
Subject: Re: [PATCH v6 13/14] arm64, acpi, numa: NUMA support based on SRAT
 and SLIT

On Thu, May 12, 2016 at 08:27:08AM -0700, David Daney wrote:
> On 05/12/2016 02:49 AM, Catalin Marinas wrote:
> >On Wed, May 11, 2016 at 05:06:13PM -0700, David Daney wrote:
> >>On 05/11/2016 03:39 AM, Catalin Marinas wrote:
> [...]
> >>>
> >>>I wonder whether you could replace the get_mpidr_in_madt() function with
> >>>something like acpi_get_phys_id(). It looks like get_mpidr_in_madt()
> >>>duplicates functionality already available elsewhere.
> >>
> >>I just tried that, and it doesn't work.
> >>
> >>The problem is that this code is being run very early in the boot, and
> >>kmalloc cannot be used.  acpi_get_phys_id() and its ilk can only be used
> >>once we have working kmalloc.  We need to extract the NUMA information early
> >>like this precisely because it is needed to initializing the slab system
> >>
> >>Notice that we are using early_acpi_os_unmap_memory() et al. in
> >>get_mpidr_in_madt() explicitly for this reason.
> >>
> >>In summary: I don't think we need another revision of this patch, it is like
> >>this for a good reason.
> >
> >Slightly confusing, in another reply you said you are going to address
> >my comment. So, is it doable?
> 
> I don't think so.
> 
> My previous reply, to the thread in 0/14, was prematurely made with the
> incorrect assumption that it was a simple change.  Now, after really digging
> in to the code, and attempting to do as you suggested, I have changed my
> mind.

Would the snippet below help with avoiding any kmalloc calls? At a quick
look, it seems that it's only map_mat_entry() that ends up using
kmalloc() calls. Alternatively, exporting map_madt_entry() may work as
well.

diff --git a/drivers/acpi/processor_core.c b/drivers/acpi/processor_core.c
index 33a38d604630..77af0a7df914 100644
--- a/drivers/acpi/processor_core.c
+++ b/drivers/acpi/processor_core.c
@@ -152,6 +152,9 @@ static phys_cpuid_t map_mat_entry(acpi_handle handle, int type, u32 acpi_id)
 	struct acpi_subtable_header *header;
 	phys_cpuid_t phys_id = PHYS_CPUID_INVALID;
 
+	if (!acpi_gbl_permanent_mmap)
+		return phys_id;
+
 	if (ACPI_FAILURE(acpi_evaluate_object(handle, "_MAT", NULL, &buffer)))
 		goto exit;
 

-- 
Catalin