Hi, On Sun, Jan 29, 2023 at 01:28:43AM +0800, Jisheng Zhang wrote: > Generally, riscv ISA extensions are fixed for any specific hardware > platform, so a hart's features won't change after booting, this > chacteristic makes it straightforward to use a static branch to check > a specific ISA extension is supported or not to optimize performance. > > However, some ISA extensions such as SVPBMT and ZICBOM are handled > via. the alternative sequences. > > Basically, for ease of maintenance, we prefer to use static branches > in C code, but recently, Samuel found that the static branch usage in > cpu_relax() breaks building with CONFIG_CC_OPTIMIZE_FOR_SIZE[1]. As > Samuel pointed out, "Having a static branch in cpu_relax() is > problematic because that function is widely inlined, including in some > quite complex functions like in the VDSO. A quick measurement shows > this static branch is responsible by itself for around 40% of the jump > table." > > Samuel's findings pointed out one of a few downsides of static branches > usage in C code to handle ISA extensions detected at boot time: > static branch's metadata in the __jump_table section, which is not > discarded after ISA extensions are finalized, wastes some space. > > I want to try to solve the issue for all possible dynamic handling of > ISA extensions at boot time. Inspired by Mark[2], this patch introduces > riscv_has_extension_*() helpers, which work like static branches but > are patched using alternatives, thus the metadata can be freed after > patching. > This patch series results in boot failures when trying to boot the qemu sifive_u emulation. There are many log messages along the line of [ 0.000000] WARNING: CPU: 0 PID: 0 at arch/riscv/kernel/patch.c:63 patch_insn_write+0x222/0x2f6 [ 0.000000] Modules linked in: [ 0.000000] CPU: 0 PID: 0 Comm: swapper Tainted: G W 6.2.0-rc7-next-20230210 #1 [ 0.000000] Hardware name: SiFive HiFive Unleashed A00 (DT) [ 0.000000] epc : patch_insn_write+0x222/0x2f6 [ 0.000000] ra : patch_insn_write+0x21e/0x2f6 [ 0.000000] epc : ffffffff800068c6 ra : ffffffff800068c2 sp : ffffffff81803df0 [ 0.000000] gp : ffffffff81a1ab78 tp : ffffffff81814f80 t0 : ffffffffffffe000 [ 0.000000] t1 : 0000000000000001 t2 : 4c45203a76637369 s0 : ffffffff81803e40 [ 0.000000] s1 : 0000000000000004 a0 : 0000000000000000 a1 : ffffffffffffffff [ 0.000000] a2 : 0000000000000004 a3 : 0000000000000000 a4 : 0000000000000001 [ 0.000000] a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000052464e43 [ 0.000000] s2 : ffffffff80b4889c s3 : 000000000000082c s4 : ffffffff80b48828 [ 0.000000] s5 : 0000000000000828 s6 : ffffffff8131a0a0 s7 : 0000000000000fff [ 0.000000] s8 : 0000000008000200 s9 : ffffffff8131a520 s10: 0000000000000018 [ 0.000000] s11: 000000000000000b t3 : 0000000000000001 t4 : 000000000000000d [ 0.000000] t5 : ffffffffd8180000 t6 : ffffffff81803bc8 [ 0.000000] status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000003 [ 0.000000] [<ffffffff800068c6>] patch_insn_write+0x222/0x2f6 [ 0.000000] [<ffffffff80006a36>] patch_text_nosync+0xc/0x2a [ 0.000000] [<ffffffff80003b86>] riscv_cpufeature_patch_func+0x52/0x98 [ 0.000000] [<ffffffff80003348>] _apply_alternatives+0x46/0x86 [ 0.000000] [<ffffffff80c02d36>] apply_boot_alternatives+0x3c/0xfa [ 0.000000] [<ffffffff80c03ad8>] setup_arch+0x584/0x5b8 [ 0.000000] [<ffffffff80c0075a>] start_kernel+0xa2/0x8f8 [ 0.000000] irq event stamp: 0 [ 0.000000] hardirqs last enabled at (0): [<0000000000000000>] 0x0 [ 0.000000] hardirqs last disabled at (0): [<0000000000000000>] 0x0 [ 0.000000] softirqs last enabled at (0): [<0000000000000000>] 0x0 [ 0.000000] softirqs last disabled at (0): [<0000000000000000>] 0x0 [ 0.000000] ---[ end trace 0000000000000000 ]--- [ 0.000000] ------------[ cut here ]------------ then qemu hangs until the session is aborted. Similar messages are also seen with the "virt" emulation, but there the boot does not hang but fails to find a root device. Guenter --- bisect: # bad: [6ba8a227fd19d19779005fb66ad7562608e1df83] Add linux-next specific files for 20230210 # good: [4ec5183ec48656cec489c49f989c508b68b518e3] Linux 6.2-rc7 git bisect start 'HEAD' 'v6.2-rc7' # bad: [94613f0efc69ed41f9229ef5c294db3ec37145da] Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/cryptodev-2.6.git git bisect bad 94613f0efc69ed41f9229ef5c294db3ec37145da # bad: [8928ece68de4371dc6e1d3336d3029c1e18ae3b4] Merge branch 'for_next' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs.git git bisect bad 8928ece68de4371dc6e1d3336d3029c1e18ae3b4 # good: [78a9f460e33d103256f3abb38f02f4759710c7dc] soc: document merges git bisect good 78a9f460e33d103256f3abb38f02f4759710c7dc # good: [b35b2472ebafa29d0bbe79fbee1da6ef3c4ec619] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/qcom/linux.git git bisect good b35b2472ebafa29d0bbe79fbee1da6ef3c4ec619 # bad: [57a87a64b520c37dd49f5fde84d09a4adb391180] Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git git bisect bad 57a87a64b520c37dd49f5fde84d09a4adb391180 # good: [cfc8ba01cc84b24ec6eb293ec9fba893f7cd4581] Merge branch 'clk-next' of git://git.kernel.org/pub/scm/linux/kernel/git/clk/linux.git git bisect good cfc8ba01cc84b24ec6eb293ec9fba893f7cd4581 # good: [6acecfa485d3de955c35a18730c106ddf1e7600e] powerpc/kcsan: Add KCSAN Support git bisect good 6acecfa485d3de955c35a18730c106ddf1e7600e # good: [8a16dea453dbc3e834b162640028e505882cd11e] Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git git bisect good 8a16dea453dbc3e834b162640028e505882cd11e # good: [6be1ff430dab9fc047762b10b2c9669399ea1f37] riscv: pgtable: Fixup comment for KERN_VIRT_SIZE git bisect good 6be1ff430dab9fc047762b10b2c9669399ea1f37 # good: [e0c267e03b0c77c9ac79ac08eada41ba8eb1b95f] riscv: module: move find_section to module.h git bisect good e0c267e03b0c77c9ac79ac08eada41ba8eb1b95f # good: [e8ad17d2b5f38e595d597a3e2419d6d7cc727b17] riscv: KVM: Switch has_svinval() to riscv_has_extension_unlikely() git bisect good e8ad17d2b5f38e595d597a3e2419d6d7cc727b17 # good: [75ab93a244a516d1d3c03c4e27d5d0deff76ebfb] Merge patch series "Zbb string optimizations" git bisect good 75ab93a244a516d1d3c03c4e27d5d0deff76ebfb # bad: [9daca9a5b9ac35361ce2d8d5ec10b19b7048d6cd] Merge patch series "riscv: improve boot time isa extensions handling" git bisect bad 9daca9a5b9ac35361ce2d8d5ec10b19b7048d6cd # good: [03966594e1170303c037b0cded35c464a13a4a45] riscv: remove riscv_isa_ext_keys[] array and related usage git bisect good 03966594e1170303c037b0cded35c464a13a4a45 # first bad commit: [9daca9a5b9ac35361ce2d8d5ec10b19b7048d6cd] Merge patch series "riscv: improve boot time isa extensions handling"
