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6027 discussions

Re: [PATCH 00/15] tracepoint: Avoid double static_branch evaluation at guarded call sites

by Peter Zijlstra

On Thu, Mar 12, 2026 at 11:49:23AM -0400, Mathieu Desnoyers wrote: > On 2026-03-12 11:40, Steven Rostedt wrote: > > On Thu, 12 Mar 2026 11:28:07 -0400 > > Mathieu Desnoyers <mathieu.desnoyers(a)efficios.com> wrote: > > > > > > Note, Vineeth came up with the naming. I would have done "do" but when I > > > > saw "invoke" I thought it sounded better. > > > > > > It works as long as you don't have a tracing subsystem called > > > "invoke", then you get into identifier clash territory. > > > > True. Perhaps we should do the double underscore trick. > > > > Instead of: trace_invoke_foo() > > > > use: trace_invoke__foo() > > > > > > Which will make it more visible to what the trace event is. > > > > Hmm, we probably should have used: trace__foo() for all tracepoints, as > > there's still functions that are called trace_foo() that are not > > tracepoints :-p > > One certain way to eliminate identifier clash would be to go for a > prefix to "trace_", e.g. Oh, I know!, call them __do_trace_##foo(). /me runs like hell

12 hours, 3 minutes

Re: [PATCH 01/15] tracepoint: Add trace_invoke_##name() API

by Peter Zijlstra

On Thu, Mar 12, 2026 at 11:39:06AM -0400, Vineeth Remanan Pillai wrote: > On Thu, Mar 12, 2026 at 11:13 AM Steven Rostedt <rostedt(a)goodmis.org> wrote: > > > > On Thu, 12 Mar 2026 11:04:56 -0400 > > "Vineeth Pillai (Google)" <vineeth(a)bitbyteword.org> wrote: > > > > > Add trace_invoke_##name() as a companion to trace_##name(). When a > > > caller already guards a tracepoint with an explicit enabled check: > > > > > > if (trace_foo_enabled() && cond) > > > trace_foo(args); > > > > > > trace_foo() internally repeats the static_branch_unlikely() test, which > > > the compiler cannot fold since static branches are patched binary > > > instructions. This results in two static-branch evaluations for every > > > guarded call site. > > > > > > trace_invoke_##name() calls __do_trace_##name() directly, skipping the > > > redundant static-branch re-check. This avoids leaking the internal > > > __do_trace_##name() symbol into call sites while still eliminating the > > > double evaluation: > > > > > > if (trace_foo_enabled() && cond) > > > trace_invoke_foo(args); /* calls __do_trace_foo() directly */ > > > > > > Three locations are updated: > > > - __DECLARE_TRACE: invoke form omits static_branch_unlikely, retains > > > the LOCKDEP RCU-watching assertion. > > > - __DECLARE_TRACE_SYSCALL: same, plus retains might_fault(). > > > - !TRACEPOINTS_ENABLED stub: empty no-op so callers compile cleanly > > > when tracepoints are compiled out. > > > > > > Suggested-by: Steven Rostedt <rostedt(a)goodmis.org> > > > Suggested-by: Peter Zijlstra <peterz(a)infradead.org> > > > Signed-off-by: Vineeth Pillai (Google) <vineeth(a)bitbyteword.org> > > > Assisted-by: Claude:claude-sonnet-4-6 > > > > I'm guessing Claude helped with the other patches. Did it really help with this one? > > > > Claude wrote and build tested the whole series based on my guidance > and prompt :-). I verified the series before sending it out, but > claude did the initial work. That seems like an unreasonable waste of energy. You could've had claude write a Coccinelle script for you and saved a ton of tokens.

12 hours, 4 minutes

Re: [PATCH net-next v3 1/2] dma-mapping: introduce DMA_ATTR_CC_DECRYPTED for pre-decrypted memory

by Jason Gunthorpe

On Thu, Mar 12, 2026 at 10:03:37AM +0100, Jiri Pirko wrote: > >Alot of device MMIO is decrypted by nature and can't be encrypted, so > >you'd have to use both flags. eg in VFIO we'd want to do this. > > Why both flags? Why MMIO flag is not enough? You still want to hit > "if (attrs & DMA_ATTR_MMIO) {" path, don't you? Because we will eventually have both decrypted and encrypted MMIO. > I mean, CC_DECRYPTED says the memory to be mapped was explicitly > decrypted before the call. MMIO was not explicitly decrypted, it is > decrypted by definition. For me that does not fit the CC_DECRYPTED > semantics. I would say CC_DECRYPTED means that pgprot_decrypted must be used to form a PTE, and !CC_DECRYPTED means that pgprot_encrypted() was used This flag should someday flow down into the vIOMMU driver and set the corresponding C bit the IOPTE (for AMD) exactly as the pgprot does. Less about set_memory_encrypted as that is only for DRAM. Jason

15 hours, 51 minutes

I HAVE RETRIEVED MY LOCKED BTC 🥳

by Ambrose MacQuoid

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18 hours, 50 minutes

Re: [PATCH net-next v3 1/2] dma-mapping: introduce DMA_ATTR_CC_DECRYPTED for pre-decrypted memory

by Jason Gunthorpe

On Mon, Mar 09, 2026 at 06:51:21PM +0100, Jiri Pirko wrote: > Mon, Mar 09, 2026 at 04:18:57PM +0100, jgg(a)ziepe.ca wrote: > >On Mon, Mar 09, 2026 at 04:02:33PM +0200, Leon Romanovsky wrote: > >> On Mon, Mar 09, 2026 at 10:15:30AM -0300, Jason Gunthorpe wrote: > >> > On Sun, Mar 08, 2026 at 12:19:48PM +0200, Leon Romanovsky wrote: > >> > > >> > > > +/* > >> > > > + * DMA_ATTR_CC_DECRYPTED: Indicates memory that has been explicitly decrypted > >> > > > + * (shared) for confidential computing guests. The caller must have > >> > > > + * called set_memory_decrypted(). A struct page is required. > >> > > > + */ > >> > > > +#define DMA_ATTR_CC_DECRYPTED (1UL << 12) > >> > > > >> > > While adding the new attribute is fine, I would expect additional checks in > >> > > dma_map_phys() to ensure the attribute cannot be misused. For example, > >> > > WARN_ON(attrs & (DMA_ATTR_CC_DECRYPTED | DMA_ATTR_MMIO)), along with a check > >> > > that we are taking the direct path only. > >> > > >> > DECRYPYED and MMIO is something that needs to work, VFIO (inside a > >> > TVM) should be using that combination. > >> > >> So this sentence "A struct page is required" from the comment above is > >> not accurate. > > > >It would be clearer to say "Unless DMA_ATTR_MMIO is provided a struct > >page is required" > > > >We need to audit if that works properly, IIRC it does, but I don't > >remember.. Jiri? > > How can you do set_memory_decrypted if you don't have page/folio ? Alot of device MMIO is decrypted by nature and can't be encrypted, so you'd have to use both flags. eg in VFIO we'd want to do this. Jason

1 day, 3 hours

[PATCH v8 0/7] Rust bindings for gem shmem + iosys_map

by Lyude Paul

This is the next version of the shmem backed GEM objects series originally from Asahi, previously posted by Daniel Almeida. One of the major changes in this patch series is a much better interface around vmaps, which we achieve by introducing a new set of rust bindings for iosys_map. The previous version of the patch series can be found here: https://patchwork.freedesktop.org/series/156093/ This patch series may be applied on top of the driver-core/driver-core-testing branch: https://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core.git… Changelogs are per-patch Asahi Lina (2): rust: helpers: Add bindings/wrappers for dma_resv_lock rust: drm: gem: shmem: Add DRM shmem helper abstraction Lyude Paul (5): rust: drm: Add gem::impl_aref_for_gem_obj! rust: drm: gem: Add raw_dma_resv() function rust: gem: Introduce DriverObject::Args rust: drm: gem: Introduce shmem::SGTable rust: drm/gem: Add vmap functions to shmem bindings drivers/gpu/drm/nova/gem.rs | 5 +- drivers/gpu/drm/tyr/gem.rs | 3 +- rust/bindings/bindings_helper.h | 3 + rust/helpers/dma-resv.c | 13 + rust/helpers/drm.c | 56 +++- rust/helpers/helpers.c | 1 + rust/kernel/drm/gem/mod.rs | 79 +++-- rust/kernel/drm/gem/shmem.rs | 529 ++++++++++++++++++++++++++++++++ 8 files changed, 667 insertions(+), 22 deletions(-) create mode 100644 rust/helpers/dma-resv.c create mode 100644 rust/kernel/drm/gem/shmem.rs -- 2.53.0

1 day, 7 hours

[PATCH v3 0/6] dma-buf: heaps: add coherent reserved-memory heap

by Albert Esteve

This patch series adds a new dma-buf heap driver that exposes coherent, non‑reusable reserved-memory regions as named heaps, so userspace can explicitly allocate buffers from those device‑specific pools. Motivation: we want cgroup accounting for all userspace‑visible buffer allocations (DRM, v4l2, dma‑buf heaps, etc.). That’s hard to do when drivers call dma_alloc_attrs() directly because the accounting controller (memcg vs dmem) is ambiguous. The long‑term plan is to steer those paths toward dma‑buf heaps, where each heap can unambiguously charge a single controller. To reach that goal, we need a heap backend for each dma_alloc_attrs() memory type. CMA and system heaps already exist; coherent reserved‑memory was the missing piece, since many SoCs define dedicated, device‑local coherent pools in DT under /reserved-memory using "shared-dma-pool" with non‑reusable regions (i.e., not CMA) that are carved out exclusively for coherent DMA and are currently only usable by in‑kernel drivers. Because these regions are device‑dependent, each heap instance binds a heap device to its reserved‑mem region via a newly introduced helper function -namely, of_reserved_mem_device_init_with_mem()- so coherent allocations use the correct dev->dma_mem. Charging to cgroups for these buffers is intentionally left out to keep review focused on the new heap; I plan to follow up based on Eric’s [1] and Maxime’s [2] work on dmem charging from userspace. This series also makes the new heap driver modular, in line with the CMA heap change in [3]. [1] https://lore.kernel.org/all/20260218-dmabuf-heap-cma-dmem-v2-0-b249886fb7b2… [2] https://lore.kernel.org/all/20250310-dmem-cgroups-v1-0-2984c1bc9312@kernel.… [3] https://lore.kernel.org/all/20260303-dma-buf-heaps-as-modules-v3-0-24344812… Signed-off-by: Albert Esteve <aesteve(a)redhat.com> --- Changes in v3: - Reorganized changesets among patches to ensure bisectability - Removed unused dma_heap_coherent_register() leftover - Removed fallback when setting mask in coherent heap dev, since dma_set_mask() already truncates to supported masks - Moved struct rmem_assigned_device (rd) logic to of_reserved_mem_device_init_with_mem() to allow listing the device - Link to v2: https://lore.kernel.org/r/20260303-b4-dmabuf-heap-coherent-rmem-v2-0-65a465… Changes in v2: - Removed dmem charging parts - Moved coherent heap registering logic to coherent.c - Made heap device a member of struct dma_heap - Split dma_heap_add logic into create/register, to be able to access the stored heap device before registered. - Avoid platform device in favour of heap device - Added a wrapper to rmem device_init() op - Switched from late_initcall() to module_init() - Made the coherent heap driver modular - Link to v1: https://lore.kernel.org/r/20260224-b4-dmabuf-heap-coherent-rmem-v1-1-dffef4… --- Albert Esteve (5): dma-buf: dma-heap: split dma_heap_add of_reserved_mem: add a helper for rmem device_init op dma: coherent: store reserved memory coherent regions dma-buf: heaps: Add Coherent heap to dmabuf heaps dma-buf: heaps: coherent: Turn heap into a module John Stultz (1): dma-buf: dma-heap: Keep track of the heap device struct drivers/dma-buf/dma-heap.c | 138 +++++++++-- drivers/dma-buf/heaps/Kconfig | 9 + drivers/dma-buf/heaps/Makefile | 1 + drivers/dma-buf/heaps/coherent_heap.c | 417 ++++++++++++++++++++++++++++++++++ drivers/of/of_reserved_mem.c | 68 ++++-- include/linux/dma-heap.h | 5 + include/linux/dma-map-ops.h | 7 + include/linux/of_reserved_mem.h | 8 + kernel/dma/coherent.c | 34 +++ 9 files changed, 640 insertions(+), 47 deletions(-) --- base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f change-id: 20260223-b4-dmabuf-heap-coherent-rmem-91fd3926afe9 Best regards, -- Albert Esteve <aesteve(a)redhat.com>

1 day, 12 hours

Re: [PATCH] lib/scatterlist: fix sg_page_count and sg_dma_page_count

by Jason Gunthorpe

On Wed, Mar 11, 2026 at 06:53:51AM +0000, Kasireddy, Vivek wrote: > So, given the current situation, what is the right thing to do? > Should we take your patch that brings back the pages array and treat it as > a temporary fix until equivalent folio based APIs are available? IMHO, yes. It saves memory, increases performance, fixes the bug and uses the APIs properly. Jason

1 day, 15 hours

I HAVE RETRIEVED MY LOCKED BTC 🥳

by Ambrose MacQuoid

1 day, 17 hours

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2 days, 1 hour

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