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Date: Wed, 09 Sep 2020 08:38:31 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: Michael Ellerman <mpe@...erman.id.au>,
Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
Jason Gunthorpe <jgg@...pe.ca>,
John Hubbard <jhubbard@...dia.com>,
Peter Zijlstra <peterz@...radead.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
linux-mm <linux-mm@...ck.org>, Paul Mackerras <paulus@...ba.org>,
linux-sparc <sparclinux@...r.kernel.org>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>,
Will Deacon <will@...nel.org>,
linux-arch <linux-arch@...r.kernel.org>,
linux-s390 <linux-s390@...r.kernel.org>,
Vasily Gorbik <gor@...ux.ibm.com>,
Richard Weinberger <richard@....at>,
linux-x86 <x86@...nel.org>, Russell King <linux@...linux.org.uk>,
Christian Borntraeger <borntraeger@...ibm.com>,
Ingo Molnar <mingo@...hat.com>,
Catalin Marinas <catalin.marinas@....com>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Arnd Bergmann <arnd@...db.de>, Jeff Dike <jdike@...toit.com>,
linux-um <linux-um@...ts.infradead.org>,
Borislav Petkov <bp@...en8.de>,
Andy Lutomirski <luto@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
linux-arm <linux-arm-kernel@...ts.infradead.org>,
linux-power <linuxppc-dev@...ts.ozlabs.org>,
LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Mike Rapoport <rppt@...nel.org>
Subject: Re: [RFC PATCH v2 2/3] mm: make pXd_addr_end() functions
page-table entry aware
On Tue, 2020-09-08 at 16:15 +0200, Alexander Gordeev wrote:
> On Tue, Sep 08, 2020 at 10:16:49AM +0200, Christophe Leroy wrote:
> > >Yes, and also two more sources :/
> > > arch/powerpc/mm/kasan/8xx.c
> > > arch/powerpc/mm/kasan/kasan_init_32.c
> > >
> > >But these two are not quite obvious wrt pgd_addr_end() used
> > >while traversing pmds. Could you please clarify a bit?
> > >
> > >
> > >diff --git a/arch/powerpc/mm/kasan/8xx.c b/arch/powerpc/mm/kasan/8xx.c
> > >index 2784224..89c5053 100644
> > >--- a/arch/powerpc/mm/kasan/8xx.c
> > >+++ b/arch/powerpc/mm/kasan/8xx.c
> > >@@ -15,8 +15,8 @@
> > > for (k_cur = k_start; k_cur != k_end; k_cur = k_next, pmd += 2, block += SZ_8M) {
> > > pte_basic_t *new;
> > >- k_next = pgd_addr_end(k_cur, k_end);
> > >- k_next = pgd_addr_end(k_next, k_end);
> > >+ k_next = pmd_addr_end(k_cur, k_end);
> > >+ k_next = pmd_addr_end(k_next, k_end);
> >
> > No, I don't think so.
> > On powerpc32 we have only two levels, so pgd and pmd are more or
> > less the same.
> > But pmd_addr_end() as defined in include/asm-generic/pgtable-nopmd.h
> > is a no-op, so I don't think it will work.
> >
> > It is likely that this function should iterate on pgd, then you get
> > pmd = pmd_offset(pud_offset(p4d_offset(pgd)));
>
> It looks like the code iterates over single pmd table while using
> pgd_addr_end() only to skip all the middle levels and bail out
> from the loop.
>
> I would be wary for switching from pmds to pgds, since we are
> trying to minimize impact (especially functional) and the
> rework does not seem that obvious.
>
I've just tested the following change, it works and should fix the
oddity:
diff --git a/arch/powerpc/mm/kasan/8xx.c b/arch/powerpc/mm/kasan/8xx.c
index 2784224054f8..8e53ddf57b84 100644
--- a/arch/powerpc/mm/kasan/8xx.c
+++ b/arch/powerpc/mm/kasan/8xx.c
@@ -9,11 +9,12 @@
static int __init
kasan_init_shadow_8M(unsigned long k_start, unsigned long k_end, void
*block)
{
- pmd_t *pmd = pmd_off_k(k_start);
+ pgd_t *pgd = pgd_offset_k(k_start);
unsigned long k_cur, k_next;
- for (k_cur = k_start; k_cur != k_end; k_cur = k_next, pmd += 2, block
+= SZ_8M) {
+ for (k_cur = k_start; k_cur != k_end; k_cur = k_next, pgd += 2, block
+= SZ_8M) {
pte_basic_t *new;
+ pmd_t *pmd = pmd_offset(pud_offset(p4d_offset(pgd, k_cur), k_cur),
k_cur);
k_next = pgd_addr_end(k_cur, k_end);
k_next = pgd_addr_end(k_next, k_end);
diff --git a/arch/powerpc/mm/kasan/kasan_init_32.c
b/arch/powerpc/mm/kasan/kasan_init_32.c
index fb294046e00e..e5f524fa71a7 100644
--- a/arch/powerpc/mm/kasan/kasan_init_32.c
+++ b/arch/powerpc/mm/kasan/kasan_init_32.c
@@ -30,13 +30,12 @@ static void __init kasan_populate_pte(pte_t *ptep,
pgprot_t prot)
int __init kasan_init_shadow_page_tables(unsigned long k_start,
unsigned long k_end)
{
- pmd_t *pmd;
+ pgd_t *pgd = pgd_offset_k(k_start);
unsigned long k_cur, k_next;
- pmd = pmd_off_k(k_start);
-
- for (k_cur = k_start; k_cur != k_end; k_cur = k_next, pmd++) {
+ for (k_cur = k_start; k_cur != k_end; k_cur = k_next, pgd++) {
pte_t *new;
+ pmd_t *pmd = pmd_offset(pud_offset(p4d_offset(pgd, k_cur), k_cur),
k_cur);
k_next = pgd_addr_end(k_cur, k_end);
if ((void *)pmd_page_vaddr(*pmd) != kasan_early_shadow_pte)
@@ -189,16 +188,18 @@ void __init kasan_early_init(void)
unsigned long addr = KASAN_SHADOW_START;
unsigned long end = KASAN_SHADOW_END;
unsigned long next;
- pmd_t *pmd = pmd_off_k(addr);
+ pgd_t *pgd = pgd_offset_k(addr);
BUILD_BUG_ON(KASAN_SHADOW_START & ~PGDIR_MASK);
kasan_populate_pte(kasan_early_shadow_pte, PAGE_KERNEL);
do {
+ pmd_t *pmd = pmd_offset(pud_offset(p4d_offset(pgd, addr), addr),
addr);
+
next = pgd_addr_end(addr, end);
pmd_populate_kernel(&init_mm, pmd, kasan_early_shadow_pte);
- } while (pmd++, addr = next, addr != end);
+ } while (pgd++, addr = next, addr != end);
if (early_mmu_has_feature(MMU_FTR_HPTE_TABLE))
kasan_early_hash_table();
---
Christophe
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