From: Mark Rutland <mark.rutland@arm.com>
To: Xishi Qiu <qiuxishi@huawei.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Laura Abbott <labbott@fedoraproject.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Kees Cook <keescook@chromium.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
zhong jiang <zhongjiang@huawei.com>,
steve.capper@arm.com
Subject: Re: [PATCH] arm64: Allow vmalloc regions to be set with set_memory_*
Date: Thu, 28 Jan 2016 10:51:39 +0000 [thread overview]
Message-ID: <20160128105138.GE17123@leverpostej> (raw)
In-Reply-To: <56A97328.9070003@huawei.com>
On Thu, Jan 28, 2016 at 09:47:20AM +0800, Xishi Qiu wrote:
> On 2016/1/18 19:56, Mark Rutland wrote:
> > On Wed, Jan 13, 2016 at 05:10:31PM +0100, Ard Biesheuvel wrote:
> >> Something along these lines, perhaps?
> >>
> >> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> >> index 3571c7309c5e..bda0a776c58e 100644
> >> --- a/arch/arm64/mm/pageattr.c
> >> +++ b/arch/arm64/mm/pageattr.c
> >> @@ -13,6 +13,7 @@
> >> #include <linux/kernel.h>
> >> #include <linux/mm.h>
> >> #include <linux/module.h>
> >> +#include <linux/vmalloc.h>
> >> #include <linux/sched.h>
> >>
> >> #include <asm/pgtable.h>
> >> @@ -44,6 +45,7 @@ static int change_memory_common(unsigned long addr
> >> unsigned long end = start + size;
> >> int ret;
> >> struct page_change_data data;
> >> + struct vm_struct *area;
> >>
> >> if (!PAGE_ALIGNED(addr)) {
> >> start &= PAGE_MASK;
> >> @@ -51,10 +53,14 @@ static int change_memory_common(unsigned long addr,
> >> WARN_ON_ONCE(1);
> >> }
> >>
> >> - if (start < MODULES_VADDR || start >= MODULES_END)
> >> - return -EINVAL;
> >> -
> >> - if (end < MODULES_VADDR || end >= MODULES_END)
> >> + /*
> >> + * Check whether the [addr, addr + size) interval is entirely
> >> + * covered by precisely one VM area that has the VM_ALLOC flag set
> >> + */
> >> + area = find_vm_area((void *)addr);
> >> + if (!area ||
> >> + end > (unsigned long)area->addr + area->size ||
> >> + !(area->flags & VM_ALLOC))
> >> return -EINVAL;
> >>
> >> data.set_mask = set_mask;
> >
> > Neat. That fixes the fencepost bug too.
> >
> > Looks good to me, though as Laura suggested we should have a comment as
> > to why we limit changes to such regions. Fancy taking her wording below
> > and spinning this as a patch?
> >
> >>>> + /*
> >>>> + * This check explicitly excludes most kernel memory. Most kernel
> >>>> + * memory is mapped with a larger page size and breaking down the
> >>>> + * larger page size without causing TLB conflicts is very difficult.
> >>>> + *
> >>>> + * If you need to call set_memory_* on a range, the recommendation is
> >>>> + * to use vmalloc since that range is mapped with pages.
> >>>> + */
> >
> > Thanks,
> > Mark.
> >
>
> Hi Mark,
>
> After change the flag, it calls only flush_tlb_kernel_range(), so why not use
> cpu_replace_ttbr1(swapper_pg_dir)?
We cannot use cpu_replace_ttbr1 here. Other CPUs may be online, and we
have no mechanism to place them in a safe set of page tables while
swapping TTBR1, we'd have to perform a deep copy of tables, and this
would be horrendously expensive.
Using flush_tlb_kernel_range() is sufficient. As modules don't share a
page or section mapping with other users, we can follow a
Break-Before-Make approach. Additionally, they're mapped at page
granularity so we never split or fuse sections anyway. We only modify
the permission bits.
> One more question, does TLB conflict only affect kernel page talbe?
It's harder to solve for the text/linear map as we can't do
Break-Before-Make without potentially unmapping something in active use
(e.g. the code used to implement Break-Before-Make).
> There is no problem when spliting the transparent hugepage, right?
There was a potential problem with huge pages causing TLB conflicts,
which didn't always seem to follow a Break-Before-Make approach.
I believe that Kirill Shutemov's recent THP rework means that
section->table and table->section conversions always go via an invalid
entry, with appropriate TLB invalidation, making that safe. I have not
yet had the chance to verify that yet, however.
Thanks,
Mark.
next prev parent reply other threads:[~2016-01-28 10:52 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-12 21:46 [PATCH] arm64: Allow vmalloc regions to be set with set_memory_* Laura Abbott
2016-01-13 0:01 ` Alexei Starovoitov
2016-01-13 0:31 ` Daniel Borkmann
2016-01-13 14:03 ` Ard Biesheuvel
2016-01-13 16:10 ` Ard Biesheuvel
2016-01-14 23:01 ` Laura Abbott
2016-01-18 11:56 ` Mark Rutland
2016-01-28 1:47 ` Xishi Qiu
2016-01-28 10:51 ` Mark Rutland [this message]
2016-01-28 11:47 ` Xishi Qiu
2016-01-28 14:27 ` Mark Rutland
2016-01-29 1:21 ` Xishi Qiu
2016-01-29 11:02 ` Mark Rutland
2016-01-30 2:48 ` Xishi Qiu
2016-02-03 13:43 ` Mark Rutland
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160128105138.GE17123@leverpostej \
--to=mark.rutland@arm.com \
--cc=ard.biesheuvel@linaro.org \
--cc=catalin.marinas@arm.com \
--cc=keescook@chromium.com \
--cc=labbott@fedoraproject.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=qiuxishi@huawei.com \
--cc=steve.capper@arm.com \
--cc=will.deacon@arm.com \
--cc=zhongjiang@huawei.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).