From: "Kumar Kartikeya Dwivedi" <memxor@gmail.com>
To: "Tejun Heo" <tj@kernel.org>, <void@manifault.com>,
<arighi@nvidia.com>, <changwoo@igalia.com>, <ast@kernel.org>,
<andrii@kernel.org>, <daniel@iogearbox.net>,
<martin.lau@linux.dev>, <memxor@gmail.com>
Cc: <peterz@infradead.org>, <catalin.marinas@arm.com>,
<will@kernel.org>, <tglx@kernel.org>, <mingo@redhat.com>,
<bp@alien8.de>, <dave.hansen@linux.intel.com>,
<akpm@linux-foundation.org>, <david@kernel.org>,
<rppt@kernel.org>, <emil@etsalapatis.com>,
<sched-ext@lists.linux.dev>, <bpf@vger.kernel.org>,
<x86@kernel.org>, <linux-arm-kernel@lists.infradead.org>,
<linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH bpf-next] bpf: Replace scratch PTE atomically when allocating arena pages
Date: Wed, 03 Jun 2026 00:29:20 +0200 [thread overview]
Message-ID: <DIYX2UV4C7W8.212LVKLCI8WG0@gmail.com> (raw)
In-Reply-To: <20260601183728.1800490-1-tj@kernel.org>
On Mon Jun 1, 2026 at 8:37 PM CEST, Tejun Heo wrote:
> apply_range_set_cb() maps the pages for a new arena allocation and returned
> -EBUSY when the target PTE was already populated. Kernel-fault recovery
> leaves the per-arena scratch page in unallocated arena PTEs, so a later
> bpf_arena_alloc_pages() over such a page hits that -EBUSY, and every
> subsequent allocation of it fails the same way. Allocation must install the
> real page over scratch instead.
>
> Overwriting the scratch PTE in place is a valid->valid change, which arm64
> forbids without break-before-make. Route through an invalid entry instead:
> ptep_try_set() fills only a none slot, so the PTE goes scratch->none->page.
> On finding scratch, clear it and flush_tlb_before_set() before retrying. The
> new flush_tlb_before_set() is a no-op except on arches like arm64 that need
> the break-before-make TLB invalidate. The loop also copes with a concurrent
> fault re-scratching the slot.
>
> Arches without ptep_try_set() never install the scratch page, so keep the
> must-be-empty check and set_pte_at() for them.
>
> Fixes: dc11a4dba246 ("bpf: Recover arena kernel faults with scratch page")
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: David Hildenbrand <david@kernel.org>
> ---
>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
prev parent reply other threads:[~2026-06-02 22:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-01 18:37 [PATCH bpf-next] bpf: Replace scratch PTE atomically when allocating arena pages Tejun Heo
2026-06-01 20:15 ` bot+bpf-ci
2026-06-02 22:09 ` Tejun Heo
2026-06-02 22:29 ` Kumar Kartikeya Dwivedi [this message]
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=DIYX2UV4C7W8.212LVKLCI8WG0@gmail.com \
--to=memxor@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=andrii@kernel.org \
--cc=arighi@nvidia.com \
--cc=ast@kernel.org \
--cc=bp@alien8.de \
--cc=bpf@vger.kernel.org \
--cc=catalin.marinas@arm.com \
--cc=changwoo@igalia.com \
--cc=daniel@iogearbox.net \
--cc=dave.hansen@linux.intel.com \
--cc=david@kernel.org \
--cc=emil@etsalapatis.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=martin.lau@linux.dev \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=rppt@kernel.org \
--cc=sched-ext@lists.linux.dev \
--cc=tglx@kernel.org \
--cc=tj@kernel.org \
--cc=void@manifault.com \
--cc=will@kernel.org \
--cc=x86@kernel.org \
/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