linux-kernel - Re: [PATCH] arm: skip nomap memblocks while finding the lowmem/highmem boundary

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Message-Id: <20190822064406.GC18872@rapoport-lnx>
Date:   Thu, 22 Aug 2019 09:44:07 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Chester Lin <clin@...e.com>
Cc:     "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "geert@...ux-m68k.org" <geert@...ux-m68k.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "guillaume.gardet@....com" <guillaume.gardet@....com>,
        Gary Lin <GLin@...e.com>, Joey Lee <JLee@...e.com>
Subject: Re: [PATCH] arm: skip nomap memblocks while finding the
 lowmem/highmem boundary

On Thu, Aug 22, 2019 at 03:59:42AM +0000, Chester Lin wrote:
> On Thu, Aug 22, 2019 at 11:45:34AM +0800, Chester Lin wrote:
> > adjust_lowmem_bounds() checks every memblocks in order to find the boundary
> > between lowmem and highmem. However some memblocks could be marked as NOMAP
> > so they are not used by kernel, which should be skipped while calculating
> > the boundary.
> > 
> > Signed-off-by: Chester Lin <clin@...e.com>
> > ---
> >  arch/arm/mm/mmu.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> > index 426d9085396b..b86dba44d828 100644
> > --- a/arch/arm/mm/mmu.c
> > +++ b/arch/arm/mm/mmu.c
> > @@ -1181,6 +1181,9 @@ void __init adjust_lowmem_bounds(void)
> >  		phys_addr_t block_start = reg->base;
> >  		phys_addr_t block_end = reg->base + reg->size;
> >  
> > +		if (memblock_is_nomap(reg))
> > +			continue;
> > +
> >  		if (reg->base < vmalloc_limit) {
> >  			if (block_end > lowmem_limit)
> >  				/*
> > -- 
> > 2.22.0
> >
> 
> Hi Russell, Mike and Ard,
> 
> Per the discussion in the thread "[PATH] efi/arm: fix allocation failure ...",
> (https://lkml.org/lkml/2019/8/21/163), I presume that the change to disregard
> NOMAP memblocks in adjust_lowmem_bounds() should be separated as a single patch.
> 
> Please let me know if any suggestion, thank you.

Let's add this one to the series: 

>From 06a986e79d60c310c804b3e550bd50316597aec5 Mon Sep 17 00:00:00 2001
From: Mike Rapoport <rppt@...ux.ibm.com>
Date: Thu, 22 Aug 2019 09:27:40 +0300
Subject: [PATCH] arm: ensure that usable memory in bank 0 starts from a
 PMD-aligned address

The calculation of memblock_limit in adjust_lowmem_bounds() assumes that
bank 0 starts from a PMD-aligned address. However, the beginning of the
first bank may be NOMAP memory and the start of usable memory
will be not aligned to PMD boundary. In such case the memblock_limit will
be set to the end of the NOMAP region, which will prevent any memblock
allocations.

Mark the region between the end of the NOMAP area and the next PMD-aligned
address as NOMAP as well, so that the usable memory will start at
PMD-aligned address.

Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
---
 arch/arm/mm/mmu.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 4495a26..25da9b2 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1177,6 +1177,22 @@ void __init adjust_lowmem_bounds(void)
 	 */
 	vmalloc_limit = (u64)(uintptr_t)vmalloc_min - PAGE_OFFSET + PHYS_OFFSET;
 
+	/*
+	 * The first usable region must be PMD aligned. Mark its start
+	 * as MEMBLOCK_NOMAP if it isn't
+	 */
+	for_each_memblock(memory, reg) {
+		if (!memblock_is_nomap(reg)) {
+			if (!IS_ALIGNED(reg->base, PMD_SIZE)) {
+				phys_addr_t len;
+
+				len = round_up(reg->base, PMD_SIZE) - reg->base;
+				memblock_mark_nomap(reg->base, len);
+			}
+			break;
+		}
+	}
+
 	for_each_memblock(memory, reg) {
 		phys_addr_t block_start = reg->base;
 		phys_addr_t block_end = reg->base + reg->size;
-- 
2.7.4


-- 
Sincerely yours,
Mike.