Re: [PATCH v4] MIPS: mm: kmalloc tlb_vpn array to avoid stack overflow

[Gregory CLEMENT <gregory.clement@bootlin.com>]

Hello Maciej,

> From: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
>
> Owing to Config4.MMUSizeExt and VTLB/FTLB MMU features later MIPSr2+ 
> cores can have more than 64 TLB entries.  Therefore allocate an array 
> for uniquification instead of placing too small an array on the stack.
>
> Fixes: 35ad7e181541 ("MIPS: mm: tlb-r4k: Uniquify TLB entries on init")
> Co-developed-by: Maciej W. Rozycki <macro@orcam.me.uk>
> Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
> Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> Cc: stable@vger.kernel.org # v6.17+: 9f048fa48740: MIPS: mm: Prevent a TLB shutdown on initial uniquification
> Cc: stable@vger.kernel.org # v6.17+

Thanks for this patch. It allows booting on EyQ5 and EyeQ6H. However,
during the build process, I saw this new warning:

WARNING: modpost: vmlinux: section mismatch in reference: r4k_tlb_configure+0x3e4 (section: .text) -> memblock_alloc_try_nid_raw (section: .init.text)

Tested-by: Gregory CLEMENT <gregory.clement@bootlin.com>

Gregory

> ---
>  Verified with Malta/74Kf and Malta/interAptiv for initial and secondary 
> CPU bootstrap.  The PM path hasn't been covered, but is expected to be 
> the same as secondary CPU bootstrap.
>
>  NB Malta/interAptiv has issues later on in SMP boot (boots fine UP) and 
> hangs with repeated:
>
> irq 23: nobody cared (try booting with the "irqpoll" option)
> CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 6.18.0-rc1-dirty #2 NONE
>
> messages (for the CP0 timer interrupt AFAICT; GIC timer is supposed to 
> be used instead).  This will have to be bisected.
>
> Changes from v3:
>
> - Rearrange tags including stable backport ones so as to pick the original 
>   change together with this fix only.
>
> Changes from v2:
>
> - Use the bootmem allocator for early calls (CPU #0 bootstrap).
>
> - Update the change description; mark for stable backporting.
> ---
>  arch/mips/mm/tlb-r4k.c |   16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
>
> linux-mips-tlb-r4k-uniquify-tlbsize.diff
> Index: linux-macro/arch/mips/mm/tlb-r4k.c
> ===================================================================
> --- linux-macro.orig/arch/mips/mm/tlb-r4k.c
> +++ linux-macro/arch/mips/mm/tlb-r4k.c
> @@ -12,6 +12,7 @@
>  #include <linux/init.h>
>  #include <linux/sched.h>
>  #include <linux/smp.h>
> +#include <linux/memblock.h>
>  #include <linux/mm.h>
>  #include <linux/hugetlb.h>
>  #include <linux/export.h>
> @@ -524,15 +525,24 @@ static int r4k_vpn_cmp(const void *a, co
>   */
>  static void r4k_tlb_uniquify(void)
>  {
> -	unsigned long tlb_vpns[1 << MIPS_CONF1_TLBS_SIZE];
>  	int tlbsize = current_cpu_data.tlbsize;
> +	bool use_slab = slab_is_available();
>  	int start = num_wired_entries();
> +	phys_addr_t tlb_vpn_size;
> +	unsigned long *tlb_vpns;
>  	unsigned long vpn_mask;
>  	int cnt, ent, idx, i;
>  
>  	vpn_mask = GENMASK(cpu_vmbits - 1, 13);
>  	vpn_mask |= IS_ENABLED(CONFIG_64BIT) ? 3ULL << 62 : 1 << 31;
>  
> +	tlb_vpn_size = tlbsize * sizeof(*tlb_vpns);
> +	tlb_vpns = (use_slab ?
> +		    kmalloc(tlb_vpn_size, GFP_KERNEL) :
> +		    memblock_alloc_raw(tlb_vpn_size, sizeof(*tlb_vpns)));
> +	if (WARN_ON(!tlb_vpns))
> +		return; /* Pray local_flush_tlb_all() is good enough. */
> +
>  	htw_stop();
>  
>  	for (i = start, cnt = 0; i < tlbsize; i++, cnt++) {
> @@ -585,6 +595,10 @@ static void r4k_tlb_uniquify(void)
>  	tlbw_use_hazard();
>  	htw_start();
>  	flush_micro_tlb();
> +	if (use_slab)
> +		kfree(tlb_vpns);
> +	else
> +		memblock_free(tlb_vpns, tlb_vpn_size);
>  }
>  
>  /*

-- 
Grégory CLEMENT, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com