kernel/Documentation/admin-guide, branch linux-6.2.y

LoongArch: Make WriteCombine configurable for ioremap()

2023-04-26T12:30:07Z

commit 16c52e503043aed1e2a2ce38d9249de5936c1f6b upstream. LoongArch maintains cache coherency in hardware, but when paired with LS7A chipsets the WUC attribute (Weak-ordered UnCached, which is similar to WriteCombine) is out of the scope of cache coherency machanism for PCIe devices (this is a PCIe protocol violation, which may be fixed in newer chipsets). This means WUC can only used for write-only memory regions now, so this option is disabled by default, making WUC silently fallback to SUC for ioremap(). You can enable this option if the kernel is ensured to run on hardware without this bug. Kernel parameter writecombine=on/off can be used to override the Kconfig option. Cc: stable@vger.kernel.org Suggested-by: WANG Xuerui Reviewed-by: WANG Xuerui Signed-off-by: Huacai Chen Signed-off-by: Greg Kroah-Hartman

mm: memcontrol: deprecate charge moving

2023-03-10T08:29:49Z

commit da34a8484d162585e22ed8c1e4114aa2f60e3567 upstream. Charge moving mode in cgroup1 allows memory to follow tasks as they migrate between cgroups. This is, and always has been, a questionable thing to do - for several reasons. First, it's expensive. Pages need to be identified, locked and isolated from various MM operations, and reassigned, one by one. Second, it's unreliable. Once pages are charged to a cgroup, there isn't always a clear owner task anymore. Cache isn't moved at all, for example. Mapped memory is moved - but if trylocking or isolating a page fails, it's arbitrarily left behind. Frequent moving between domains may leave a task's memory scattered all over the place. Third, it isn't really needed. Launcher tasks can kick off workload tasks directly in their target cgroup. Using dedicated per-workload groups allows fine-grained policy adjustments - no need to move tasks and their physical pages between control domains. The feature was never forward-ported to cgroup2, and it hasn't been missed. Despite it being a niche usecase, the maintenance overhead of supporting it is enormous. Because pages are moved while they are live and subject to various MM operations, the synchronization rules are complicated. There are lock_page_memcg() in MM and FS code, which non-cgroup people don't understand. In some cases we've been able to shift code and cgroup API calls around such that we can rely on native locking as much as possible. But that's fragile, and sometimes we need to hold MM locks for longer than we otherwise would (pte lock e.g.). Mark the feature deprecated. Hopefully we can remove it soon. And backport into -stable kernels so that people who develop against earlier kernels are warned about this deprecation as early as possible. [akpm@linux-foundation.org: fix memory.rst underlining] Link: https://lkml.kernel.org/r/Y5COd+qXwk/S+n8N@cmpxchg.org Signed-off-by: Johannes Weiner Acked-by: Shakeel Butt Acked-by: Hugh Dickins Acked-by: Michal Hocko Cc: Muchun Song Cc: Roman Gushchin Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

docs: gdbmacros: print newest record

2023-03-10T08:29:49Z

commit f2e4cca2f670c8e52fbb551a295f2afc9aa2bd72 upstream. @head_id points to the newest record, but the printing loop exits when it increments to this value (before printing). Exit the printing loop after the newest record has been printed. The python-based function in scripts/gdb/linux/dmesg.py already does this correctly. Fixes: e60768311af8 ("scripts/gdb: update for lockless printk ringbuffer") Cc: stable@vger.kernel.org Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20221229134339.197627-1-john.ogness@linutronix.de Signed-off-by: Greg Kroah-Hartman

Documentation/hw-vuln: Document the interaction between IBRS and STIBP

2023-03-10T08:29:36Z

commit e02b50ca442e88122e1302d4dbc1b71a4808c13f upstream. Explain why STIBP is needed with legacy IBRS as currently implemented (KERNEL_IBRS) and why STIBP is not needed when enhanced IBRS is enabled. Fixes: 7c693f54c873 ("x86/speculation: Add spectre_v2=ibrs option to support Kernel IBRS") Signed-off-by: KP Singh Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20230227060541.1939092-2-kpsingh@kernel.org Signed-off-by: Greg Kroah-Hartman

Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

2023-02-18T19:07:32Z

Pull kvm/x86 fixes from Paolo Bonzini: - zero all padding for KVM_GET_DEBUGREGS - fix rST warning - disable vPMU support on hybrid CPUs * tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: kvm: initialize all of the kvm_debugregs structure before sending it to userspace perf/x86: Refuse to export capabilities for hybrid PMUs KVM: x86/pmu: Disable vPMU support on hybrid CPUs (host PMUs) Documentation/hw-vuln: Fix rST warning

Documentation/hw-vuln: Fix rST warning

2023-02-15T12:24:23Z

The following warning: Documentation/admin-guide/hw-vuln/cross-thread-rsb.rst:92: ERROR: Unexpected indentation. was introduced by commit 493a2c2d23ca. Fix it by placing everything in the same paragraph and also use a monospace font. Fixes: 493a2c2d23ca ("Documentation/hw-vuln: Add documentation for Cross-Thread Return Predictions") Reported-by: Stephen Rothwell Signed-off-by: Paolo Bonzini

Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

2023-02-14T17:17:01Z

Pull kvm fixes from Paolo Bonzini: "Certain AMD processors are vulnerable to a cross-thread return address predictions bug. When running in SMT mode and one of the sibling threads transitions out of C0 state, the other thread gets access to twice as many entries in the RSB, but unfortunately the predictions of the now-halted logical processor are not purged. Therefore, the executing processor could speculatively execute from locations that the now-halted processor had trained the RSB on. The Spectre v2 mitigations cover the Linux kernel, as it fills the RSB when context switching to the idle thread. However, KVM allows a VMM to prevent exiting guest mode when transitioning out of C0 using the KVM_CAP_X86_DISABLE_EXITS capability can be used by a VMM to change this behavior. To mitigate the cross-thread return address predictions bug, a VMM must not be allowed to override the default behavior to intercept C0 transitions. These patches introduce a KVM module parameter that, if set, will prevent the user from disabling the HLT, MWAIT and CSTATE exits" * tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: Documentation/hw-vuln: Add documentation for Cross-Thread Return Predictions KVM: x86: Mitigate the cross-thread return address predictions bug x86/speculation: Identify processors vulnerable to SMT RSB predictions

Documentation/hw-vuln: Add documentation for Cross-Thread Return Predictions

2023-02-10T12:27:37Z

Add the admin guide for the Cross-Thread Return Predictions vulnerability. Signed-off-by: Tom Lendacky Message-Id: <60f9c0b4396956ce70499ae180cb548720b25c7e.1675956146.git.thomas.lendacky@amd.com> Signed-off-by: Paolo Bonzini

Revert "mm: add nodes= arg to memory.reclaim"

2023-02-01T00:44:07Z

This reverts commit 12a5d3955227b0d7e04fb793ccceeb2a1dd275c5. Although it is recognized that a finer grained pro-active reclaim is something we need and want the semantic of this implementation is really ambiguous. In a follow up discussion it became clear that there are two essential usecases here. One is to use memory.reclaim to pro-actively reclaim memory and expectation is that the requested and reported amount of memory is uncharged from the memcg. Another usecase focuses on pro-active demotion when the memory is merely shuffled around to demotion targets while the overall charged memory stays unchanged. The current implementation considers demoted pages as reclaimed and that break both usecases. [1] has tried to address the reporting part but there are more issues with that summarized in [2] and follow up emails. Let's revert the nodemask based extension of the memcg pro-active reclaim for now until we settle with a more robust semantic. [1] http://lkml.kernel.org/r/http://lkml.kernel.org/r/20221206023406.3182800-1-almasrymina@google.com [2] http://lkml.kernel.org/r/Y5bsmpCyeryu3Zz1@dhcp22.suse.cz Link: https://lkml.kernel.org/r/Y5xASNe1x8cusiTx@dhcp22.suse.cz Fixes: 12a5d3955227b0d ("mm: add nodes= arg to memory.reclaim") Signed-off-by: Michal Hocko Cc: Bagas Sanjaya Cc: Huang Ying Cc: Johannes Weiner Cc: Jonathan Corbet Cc: Mina Almasry Cc: Muchun Song Cc: Roman Gushchin Cc: Shakeel Butt Cc: Tejun Heo Cc: Wei Xu Cc: Yang Shi Cc: Yosry Ahmed Cc: zefan li Signed-off-by: Andrew Morton

Docs/admin-guide/mm/zswap: remove zsmalloc's lack of writeback warning

2023-01-12T00:14:21Z

Writeback has been implemented for zsmalloc, so this warning no longer holds. Link: https://lkml.kernel.org/r/20230106220016.172303-1-nphamcs@gmail.com Fixes: 9997bc017549a ("zsmalloc: implement writeback mechanism for zsmalloc") Suggested-by: Thomas Weißschuh Signed-off-by: Nhat Pham Reviewed-by: Sergey Senozhatsky Cc: Johannes Weiner Cc: Jonathan Corbet Signed-off-by: Andrew Morton