On 2015/2/26 23:12, Andy Lutomirski wrote: > On Thu, Feb 26, 2015 at 5:12 AM, tip-bot for Wang Nan <tipbot@xxxxxxxxx> wrote: >> Commit-ID: b4d8327024637cb2a1f7910dcb5d0ad7a096f473 >> Gitweb: http://git.kernel.org/tip/b4d8327024637cb2a1f7910dcb5d0ad7a096f473 >> Author: Wang Nan <wangnan0@xxxxxxxxxx> >> AuthorDate: Thu, 26 Feb 2015 13:49:39 +0800 >> Committer: Ingo Molnar <mingo@xxxxxxxxxx> >> CommitDate: Thu, 26 Feb 2015 12:29:20 +0100 >> >> x86/traps: Enable DEBUG_STACK after cpu_init() for TRAP_DB/BP >> >> Before this patch early_trap_init() installs DEBUG_STACK for >> X86_TRAP_BP and X86_TRAP_DB. However, DEBUG_STACK doesn't work >> correctly until cpu_init() <-- trap_init(). >> >> This patch passes 0 to set_intr_gate_ist() and >> set_system_intr_gate_ist() instead of DEBUG_STACK to let it use >> same stack as kernel, and installs DEBUG_STACK for them in >> trap_init(). >> > > Sorry, I'm late to the party. This patch, while technically correct > AFAICT, is really ugly, because the whole point is that it *doesn't* > use ist. In other words: > >> + set_intr_gate_ist(X86_TRAP_DB, &debug, 0); > > That should be set_intr_gate(X86_TRAP_DB, &debug); > I considered this, but found that set_intr_gate() and set_intr_gate_ist(..., 0) behaviors differently: set_intr_gate() -> _trace_set_gate() requires 'trace_##addr' to be installed to trace_idt_table, while set_intr_gate_ist(..., 0) puts 'addr'. into trace_idt_table() through _set_gate(). Therefore, if we want to use set_intr_gate() we need to provide a trace_debug entry for it, which will be overwritten in trap_init() so it is in fact a useless symbol. Anyway, I'd like to post a v3 patch follow your advise. Please keep an eye on it. Thank you! >> /* int3 can be called from all */ >> - set_system_intr_gate_ist(X86_TRAP_BP, &int3, DEBUG_STACK); >> + set_system_intr_gate_ist(X86_TRAP_BP, &int3, 0); > > Similarly, this should be set_system_gate. > >> #ifdef CONFIG_X86_32 >> set_intr_gate(X86_TRAP_PF, page_fault); >> #endif >> @@ -1005,6 +1013,15 @@ void __init trap_init(void) >> */ >> cpu_init(); >> >> + /* >> + * X86_TRAP_DB and X86_TRAP_BP have been set >> + * in early_trap_init(). However, DEBUG_STACK works only after >> + * cpu_init() loads TSS. See comments in early_trap_init(). > > It's not that DEBUG_STACK only works after the TSS is loaded; it's > that the IST mechanism only works after TSS is loaded. > > --Andy > -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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