From: Mike Rapoport <rppt@kernel•org>
To: Kevin Brodsky <kevin.brodsky@arm•com>
Cc: linux-mm@kvack•org, linux-kernel@vger•kernel.org,
Alexander Gordeev <agordeev@linux•ibm.com>,
Andreas Larsson <andreas@gaisler•com>,
Andrew Morton <akpm@linux-foundation•org>,
Boris Ostrovsky <boris.ostrovsky@oracle•com>,
Borislav Petkov <bp@alien8•de>,
Catalin Marinas <catalin.marinas@arm•com>,
Christophe Leroy <christophe.leroy@csgroup•eu>,
Dave Hansen <dave.hansen@linux•intel.com>,
David Hildenbrand <david@redhat•com>,
"David S. Miller" <davem@davemloft•net>,
"H. Peter Anvin" <hpa@zytor•com>, Ingo Molnar <mingo@redhat•com>,
Jann Horn <jannh@google•com>, Juergen Gross <jgross@suse•com>,
"Liam R. Howlett" <Liam.Howlett@oracle•com>,
Lorenzo Stoakes <lorenzo.stoakes@oracle•com>,
Madhavan Srinivasan <maddy@linux•ibm.com>,
Michael Ellerman <mpe@ellerman•id.au>,
Michal Hocko <mhocko@suse•com>,
Nicholas Piggin <npiggin@gmail•com>,
Peter Zijlstra <peterz@infradead•org>,
Ryan Roberts <ryan.roberts@arm•com>,
Suren Baghdasaryan <surenb@google•com>,
Thomas Gleixner <tglx@linutronix•de>,
Vlastimil Babka <vbabka@suse•cz>, Will Deacon <will@kernel•org>,
linux-arm-kernel@lists•infradead.org,
linuxppc-dev@lists•ozlabs.org, sparclinux@vger•kernel.org,
xen-devel@lists•xenproject.org
Subject: Re: [PATCH 2/7] mm: introduce local state for lazy_mmu sections
Date: Fri, 5 Sep 2025 14:19:11 +0300 [thread overview]
Message-ID: <aLrHL-C_UXfUbCd9@kernel.org> (raw)
In-Reply-To: <20250904125736.3918646-3-kevin.brodsky@arm.com>
On Thu, Sep 04, 2025 at 01:57:31PM +0100, Kevin Brodsky wrote:
> arch_{enter,leave}_lazy_mmu_mode() currently have a stateless API
> (taking and returning no value). This is proving problematic in
> situations where leave() needs to restore some context back to its
> original state (before enter() was called). In particular, this
> makes it difficult to support the nesting of lazy_mmu sections -
> leave() does not know whether the matching enter() call occurred
> while lazy_mmu was already enabled, and whether to disable it or
> not.
>
> This patch gives all architectures the chance to store local state
> while inside a lazy_mmu section by making enter() return some value,
> storing it in a local variable, and having leave() take that value.
> That value is typed lazy_mmu_state_t - each architecture defining
> __HAVE_ARCH_ENTER_LAZY_MMU_MODE is free to define it as it sees fit.
> For now we define it as int everywhere, which is sufficient to
> support nesting.
>
> The diff is unfortunately rather large as all the API changes need
> to be done atomically. Main parts:
>
> * Changing the prototypes of arch_{enter,leave}_lazy_mmu_mode()
> in generic and arch code, and introducing lazy_mmu_state_t.
>
> * Introducing LAZY_MMU_{DEFAULT,NESTED} for future support of
> nesting. enter() always returns LAZY_MMU_DEFAULT for now.
> (linux/mm_types.h is not the most natural location for defining
> those constants, but there is no other obvious header that is
> accessible where arch's implement the helpers.)
>
> * Changing all lazy_mmu sections to introduce a lazy_mmu_state
> local variable, having enter() set it and leave() take it. Most of
> these changes were generated using the Coccinelle script below.
>
> @@
> @@
> {
> + lazy_mmu_state_t lazy_mmu_state;
> ...
> - arch_enter_lazy_mmu_mode();
> + lazy_mmu_state = arch_enter_lazy_mmu_mode();
> ...
> - arch_leave_lazy_mmu_mode();
> + arch_leave_lazy_mmu_mode(lazy_mmu_state);
> ...
> }
>
> Note: it is difficult to provide a default definition of
> lazy_mmu_state_t for architectures implementing lazy_mmu, because
> that definition would need to be available in
> arch/x86/include/asm/paravirt_types.h and adding a new generic
> #include there is very tricky due to the existing header soup.
>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm•com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel•org>
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2025-09-05 11:19 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-04 12:57 [PATCH 0/7] Nesting support for lazy MMU mode Kevin Brodsky
2025-09-04 12:57 ` [PATCH 1/7] mm: remove arch_flush_lazy_mmu_mode() Kevin Brodsky
2025-09-05 11:00 ` Mike Rapoport
2025-09-04 12:57 ` [PATCH 2/7] mm: introduce local state for lazy_mmu sections Kevin Brodsky
2025-09-04 15:06 ` Yeoreum Yun
2025-09-04 15:47 ` Kevin Brodsky
2025-09-04 17:28 ` Lorenzo Stoakes
2025-09-04 22:14 ` Kevin Brodsky
2025-09-05 11:21 ` Lorenzo Stoakes
2025-09-05 11:37 ` Lorenzo Stoakes
2025-09-05 12:22 ` Kevin Brodsky
2025-09-05 11:19 ` Mike Rapoport [this message]
2025-09-04 12:57 ` [PATCH 3/7] arm64: mm: fully support nested " Kevin Brodsky
2025-09-04 12:57 ` [PATCH 4/7] x86/xen: support nested lazy_mmu sections (again) Kevin Brodsky
2025-09-05 15:48 ` Alexander Gordeev
2025-09-08 7:32 ` Kevin Brodsky
2025-09-04 12:57 ` [PATCH 5/7] powerpc/mm: support nested lazy_mmu sections Kevin Brodsky
2025-09-05 15:52 ` Alexander Gordeev
2025-09-08 7:32 ` Kevin Brodsky
2025-09-04 12:57 ` [PATCH 6/7] sparc/mm: " Kevin Brodsky
2025-09-04 12:57 ` [PATCH 7/7] mm: update lazy_mmu documentation Kevin Brodsky
2025-09-05 11:13 ` Mike Rapoport
2025-09-05 9:46 ` [PATCH 0/7] Nesting support for lazy MMU mode Alexander Gordeev
2025-09-05 12:11 ` Kevin Brodsky
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=aLrHL-C_UXfUbCd9@kernel.org \
--to=rppt@kernel$(echo .)org \
--cc=Liam.Howlett@oracle$(echo .)com \
--cc=agordeev@linux$(echo .)ibm.com \
--cc=akpm@linux-foundation$(echo .)org \
--cc=andreas@gaisler$(echo .)com \
--cc=boris.ostrovsky@oracle$(echo .)com \
--cc=bp@alien8$(echo .)de \
--cc=catalin.marinas@arm$(echo .)com \
--cc=christophe.leroy@csgroup$(echo .)eu \
--cc=dave.hansen@linux$(echo .)intel.com \
--cc=davem@davemloft$(echo .)net \
--cc=david@redhat$(echo .)com \
--cc=hpa@zytor$(echo .)com \
--cc=jannh@google$(echo .)com \
--cc=jgross@suse$(echo .)com \
--cc=kevin.brodsky@arm$(echo .)com \
--cc=linux-arm-kernel@lists$(echo .)infradead.org \
--cc=linux-kernel@vger$(echo .)kernel.org \
--cc=linux-mm@kvack$(echo .)org \
--cc=linuxppc-dev@lists$(echo .)ozlabs.org \
--cc=lorenzo.stoakes@oracle$(echo .)com \
--cc=maddy@linux$(echo .)ibm.com \
--cc=mhocko@suse$(echo .)com \
--cc=mingo@redhat$(echo .)com \
--cc=mpe@ellerman$(echo .)id.au \
--cc=npiggin@gmail$(echo .)com \
--cc=peterz@infradead$(echo .)org \
--cc=ryan.roberts@arm$(echo .)com \
--cc=sparclinux@vger$(echo .)kernel.org \
--cc=surenb@google$(echo .)com \
--cc=tglx@linutronix$(echo .)de \
--cc=vbabka@suse$(echo .)cz \
--cc=will@kernel$(echo .)org \
--cc=xen-devel@lists$(echo .)xenproject.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
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