kernel.git/arch/x86/kernel/alternative.c, branch linux-5.13.y

x86/alternative: Optimize single-byte NOPs at an arbitrary position

2021-06-03T14:33:09Z

Up until now the assumption was that an alternative patching site would have some instructions at the beginning and trailing single-byte NOPs (0x90) padding. Therefore, the patching machinery would go and optimize those single-byte NOPs into longer ones. However, this assumption is broken on 32-bit when code like hv_do_hypercall() in hyperv_init() would use the ratpoline speculation killer CALL_NOSPEC. The 32-bit version of that macro would align certain insns to 16 bytes, leading to the compiler issuing a one or more single-byte NOPs, depending on the holes it needs to fill for alignment. That would lead to the warning in optimize_nops() to fire: ------------[ cut here ]------------ Not a NOP at 0xc27fb598 WARNING: CPU: 0 PID: 0 at arch/x86/kernel/alternative.c:211 optimize_nops.isra.13 due to that function verifying whether all of the following bytes really are single-byte NOPs. Therefore, carve out the NOP padding into a separate function and call it for each NOP range beginning with a single-byte NOP. Fixes: 23c1ad538f4f ("x86/alternatives: Optimize optimize_nops()") Reported-by: Richard Narron Signed-off-by: Borislav Petkov Acked-by: Peter Zijlstra (Intel) Link: https://bugzilla.kernel.org/show_bug.cgi?id=213301 Link: https://lkml.kernel.org/r/20210601212125.17145-1-bp@alien8.de

Merge tag 'x86-mm-2021-04-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2021-04-29T18:41:43Z

Pull x86 tlb updates from Ingo Molnar: "The x86 MM changes in this cycle were: - Implement concurrent TLB flushes, which overlaps the local TLB flush with the remote TLB flush. In testing this improved sysbench performance measurably by a couple of percentage points, especially if TLB-heavy security mitigations are active. - Further micro-optimizations to improve the performance of TLB flushes" * tag 'x86-mm-2021-04-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: smp: Micro-optimize smp_call_function_many_cond() smp: Inline on_each_cpu_cond() and on_each_cpu() x86/mm/tlb: Remove unnecessary uses of the inline keyword cpumask: Mark functions as pure x86/mm/tlb: Do not make is_lazy dirty for no reason x86/mm/tlb: Privatize cpu_tlbstate x86/mm/tlb: Flush remote and local TLBs concurrently x86/mm/tlb: Open-code on_each_cpu_cond_mask() for tlb_is_not_lazy() x86/mm/tlb: Unify flush_tlb_func_local() and flush_tlb_func_remote() smp: Run functions concurrently in smp_call_function_many_cond()

x86/alternatives: Optimize optimize_nops()

2021-04-02T10:41:17Z

Currently, optimize_nops() scans to see if the alternative starts with NOPs. However, the emit pattern is: 141: \oldinstr 142: .skip (len-(142b-141b)), 0x90 That is, when 'oldinstr' is short, the tail is padded with NOPs. This case never gets optimized. Rewrite optimize_nops() to replace any trailing string of NOPs inside the alternative to larger NOPs. Also run it irrespective of patching, replacing NOPs in both the original and replaced code. A direct consequence is that 'padlen' becomes superfluous, so remove it. [ bp: - Adjust commit message - remove a stale comment about needing to pad - add a comment in optimize_nops() - exit early if the NOP verif. loop catches a mismatch - function should not not add NOPs in that case - fix the "optimized NOPs" offsets output ] Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Borislav Petkov Signed-off-by: Ingo Molnar Link: https://lkml.kernel.org/r/20210326151259.442992235@infradead.org

Merge branch 'x86/cpu' into WIP.x86/core, to merge the NOP changes & resolve a semantic conflict

2021-04-02T10:36:30Z

Conflict-merge this main commit in essence: a89dfde3dc3c: ("x86: Remove dynamic NOP selection") With this upstream commit: b90829704780: ("bpf: Use NOP_ATOMIC5 instead of emit_nops(&prog, 5) for BPF_TRAMP_F_CALL_ORIG") Semantic merge conflict: arch/x86/net/bpf_jit_comp.c - memcpy(prog, ideal_nops[NOP_ATOMIC5], X86_PATCH_SIZE); + memcpy(prog, x86_nops[5], X86_PATCH_SIZE); Signed-off-by: Ingo Molnar

Merge 'x86/alternatives'

2021-03-31T16:04:19Z

Pick up dependent changes. Signed-off-by: Borislav Petkov

x86: Add insn_decode_kernel()

2021-03-31T14:20:22Z

Add a helper to decode kernel instructions; there's no point in endlessly repeating those last two arguments. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Borislav Petkov Link: https://lkml.kernel.org/r/20210326151259.379242587@infradead.org

x86: Remove dynamic NOP selection

2021-03-15T15:24:59Z

This ensures that a NOP is a NOP and not a random other instruction that is also a NOP. It allows simplification of dynamic code patching that wants to verify existing code before writing new instructions (ftrace, jump_label, static_call, etc..). Differentiating on NOPs is not a feature. This pessimises 32bit (DONTCARE) and 32bit on 64bit CPUs (CARELESS). 32bit is not a performance target. Everything x86_64 since AMD K10 (2007) and Intel IvyBridge (2012) is fine with using NOPL (as opposed to prefix NOP). And per FEATURE_NOPL being required for x86_64, all x86_64 CPUs can use NOPL. So stop caring about NOPs, simplify things and get on with life. [ The problem seems to be that some uarchs can only decode NOPL on a single front-end port while others have severe decode penalties for excessive prefixes. All modern uarchs can handle both, except Atom, which has prefix penalties. ] [ Also, much doubt you can actually measure any of this on normal workloads. ] After this, FEATURE_NOPL is unused except for required-features for x86_64. FEATURE_K8 is only used for PTI. [ bp: Kernel build measurements showed ~0.3s slowdown on Sandybridge which is hardly a slowdown. Get rid of X86_FEATURE_K7, while at it. ] Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Borislav Petkov Acked-by: Alexei Starovoitov # bpf Acked-by: Linus Torvalds Link: https://lkml.kernel.org/r/20210312115749.065275711@infradead.org

x86/alternative: Use insn_decode()

2021-03-15T10:25:38Z

No functional changes, just simplification. Signed-off-by: Borislav Petkov Link: https://lkml.kernel.org/r/20210304174237.31945-10-bp@alien8.de

x86/paravirt: Have only one paravirt patch function

2021-03-11T19:11:09Z

There is no need any longer to have different paravirt patch functions for native and Xen. Eliminate native_patch() and rename paravirt_patch_default() to paravirt_patch(). Signed-off-by: Juergen Gross Signed-off-by: Borislav Petkov Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20210311142319.4723-15-jgross@suse.com

x86/paravirt: Add new features for paravirt patching

2021-03-11T18:51:49Z

For being able to switch paravirt patching from special cased custom code sequences to ALTERNATIVE handling some X86_FEATURE_* are needed as new features. This enables to have the standard indirect pv call as the default code and to patch that with the non-Xen custom code sequence via ALTERNATIVE patching later. Make sure paravirt patching is performed before alternatives patching. Signed-off-by: Juergen Gross Signed-off-by: Borislav Petkov Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20210311142319.4723-9-jgross@suse.com