| Message ID | 1552431636-31511-10-git-send-email-fenghua.yu@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | x86/split_lock: Enable #AC exception for split locked accesses | expand |
On 3/12/19 4:00 PM, Fenghua Yu wrote: > +#ifndef CONFIG_CPU_SUP_INTEL > DO_ERROR(X86_TRAP_AC, SIGBUS, BUS_ADRALN, NULL, "alignment check", alignment_check) > +#else > +dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code) > +{ > + unsigned int trapnr = X86_TRAP_AC; > + char str[] = "alignment check"; > + int signr = SIGBUS; > + > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > + > + if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) != > + NOTIFY_STOP) { > + cond_local_irq_enable(regs); > + if (!user_mode(regs)) { > + /* > + * Only split lock can generate #AC from kernel. Warn > + * and disable #AC for split lock on current CPU. > + */ > + msr_clear_bit(MSR_TEST_CTL, > + TEST_CTL_ENABLE_SPLIT_LOCK_DETECT_SHIFT) I don't see any feature checking here. Don't we need to see if this MSR is supported? Shouldn't the code here on systems that don't support split lock disabling be the same as on CONFIG_CPU_SUP_INTEL=n systems? > + WARN_ONCE(1, "A split lock issue is detected.\n"); > + > + return; > + } > + /* Handle #AC generated from user code. */ > + do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs, > + error_code, BUS_ADRALN, NULL); > + } > +} > +#endif So... Do we really need an Intel-specific #ifdef for this sucker?
On Tue, Mar 12, 2019 at 04:51:22PM -0700, Dave Hansen wrote: > On 3/12/19 4:00 PM, Fenghua Yu wrote: > I don't see any feature checking here. Don't we need to see if this MSR > is supported? > > Shouldn't the code here on systems that don't support split lock > disabling be the same as on CONFIG_CPU_SUP_INTEL=n systems? You are right. Is the following #AC handler code better? diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index d26f9e9c3d83..5296021509c7 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -61,6 +61,7 @@ #include <asm/mpx.h> #include <asm/vm86.h> #include <asm/umip.h> +#include <asm/cpu.h> #ifdef CONFIG_X86_64 #include <asm/x86_init.h> @@ -293,7 +294,37 @@ DO_ERROR(X86_TRAP_OLD_MF, SIGFPE, 0, NULL, "coprocessor segment overru DO_ERROR(X86_TRAP_TS, SIGSEGV, 0, NULL, "invalid TSS", invalid_TSS) DO_ERROR(X86_TRAP_NP, SIGBUS, 0, NULL, "segment not present", segment_not_present) DO_ERROR(X86_TRAP_SS, SIGBUS, 0, NULL, "stack segment", stack_segment) -DO_ERROR(X86_TRAP_AC, SIGBUS, BUS_ADRALN, NULL, "alignment check", alignment_check) +dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code) +{ + unsigned int trapnr = X86_TRAP_AC; + char str[] = "alignment check"; + int signr = SIGBUS; + + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); + + if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) != + NOTIFY_STOP) { + cond_local_irq_enable(regs); + if (!user_mode(regs)) { + if (!this_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT)) + return; + + /* + * Only split lock can generate #AC from kernel. Warn + * and disable #AC for split lock on current CPU. + */ + msr_clear_bit(MSR_TEST_CTL, + TEST_CTL_ENABLE_SPLIT_LOCK_DETECT_SHIFT); + WARN_ONCE(1, "A split lock issue is detected.\n"); + + + return; + } + /* Handle #AC generated from user code. */ + do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs, + error_code, BUS_ADRALN, NULL); + } +} #undef IP #ifdef CONFIG_VMAP_STACK
On 3/12/19 5:49 PM, Fenghua Yu wrote: > On Tue, Mar 12, 2019 at 04:51:22PM -0700, Dave Hansen wrote: >> On 3/12/19 4:00 PM, Fenghua Yu wrote: >> I don't see any feature checking here. Don't we need to see if this MSR >> is supported? >> >> Shouldn't the code here on systems that don't support split lock >> disabling be the same as on CONFIG_CPU_SUP_INTEL=n systems? > > You are right. Is the following #AC handler code better? Fenghua, I'd really appreciate if you could take a deep breath and slow down. The most important thing is getting the right patch out and being as respectful as possible with reviewer bandwidth. > @@ -293,7 +294,37 @@ DO_ERROR(X86_TRAP_OLD_MF, SIGFPE, 0, NULL, "coprocessor segment overru > DO_ERROR(X86_TRAP_TS, SIGSEGV, 0, NULL, "invalid TSS", invalid_TSS) > DO_ERROR(X86_TRAP_NP, SIGBUS, 0, NULL, "segment not present", segment_not_present) > DO_ERROR(X86_TRAP_SS, SIGBUS, 0, NULL, "stack segment", stack_segment) > -DO_ERROR(X86_TRAP_AC, SIGBUS, BUS_ADRALN, NULL, "alignment check", alignment_check) > +dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code) Is this really an appropriate place to stick this function? Without any whitespace, and even pushing out the "#undef" that was here before? > +{ > + unsigned int trapnr = X86_TRAP_AC; > + char str[] = "alignment check"; > + int signr = SIGBUS; > + > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); > + > + if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) != > + NOTIFY_STOP) { Please unindent this code block. > + cond_local_irq_enable(regs); > + if (!user_mode(regs)) { Comments please. The comment about #AC being impossible in the kernel without the split lock detection feature belongs here, not below. > + if (!this_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT)) > + return; Is this consistent with the code that was here before? Basically, if we are in the kernel, get an #AC and end up here, we just return from this function? Is that what DO_ERROR() did? > + /* > + * Only split lock can generate #AC from kernel. Warn > + * and disable #AC for split lock on current CPU. > + */ > + msr_clear_bit(MSR_TEST_CTL, > + TEST_CTL_ENABLE_SPLIT_LOCK_DETECT_SHIFT); > + WARN_ONCE(1, "A split lock issue is detected.\n"); Is it an issue? I'd probably say: "split lock operation detected" > + > + > + return; Extra whitespace. > + } > + /* Handle #AC generated from user code. */ > + do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs, > + error_code, BUS_ADRALN, NULL); > + } > +} > #undef IP
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index d26f9e9c3d83..69b6233e783e 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -61,6 +61,7 @@ #include <asm/mpx.h> #include <asm/vm86.h> #include <asm/umip.h> +#include <asm/cpu.h> #ifdef CONFIG_X86_64 #include <asm/x86_init.h> @@ -293,7 +294,37 @@ DO_ERROR(X86_TRAP_OLD_MF, SIGFPE, 0, NULL, "coprocessor segment overru DO_ERROR(X86_TRAP_TS, SIGSEGV, 0, NULL, "invalid TSS", invalid_TSS) DO_ERROR(X86_TRAP_NP, SIGBUS, 0, NULL, "segment not present", segment_not_present) DO_ERROR(X86_TRAP_SS, SIGBUS, 0, NULL, "stack segment", stack_segment) +#ifndef CONFIG_CPU_SUP_INTEL DO_ERROR(X86_TRAP_AC, SIGBUS, BUS_ADRALN, NULL, "alignment check", alignment_check) +#else +dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code) +{ + unsigned int trapnr = X86_TRAP_AC; + char str[] = "alignment check"; + int signr = SIGBUS; + + RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU"); + + if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) != + NOTIFY_STOP) { + cond_local_irq_enable(regs); + if (!user_mode(regs)) { + /* + * Only split lock can generate #AC from kernel. Warn + * and disable #AC for split lock on current CPU. + */ + msr_clear_bit(MSR_TEST_CTL, + TEST_CTL_ENABLE_SPLIT_LOCK_DETECT_SHIFT); + WARN_ONCE(1, "A split lock issue is detected.\n"); + + return; + } + /* Handle #AC generated from user code. */ + do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs, + error_code, BUS_ADRALN, NULL); + } +} +#endif #undef IP #ifdef CONFIG_VMAP_STACK
There may be different considerations on how to handle #AC for split lock, e.g. how to handle system hang caused by split lock issue in firmware, how to emulate faulting instruction, etc. We use a simple method to handle user and kernel split lock and may extend the method in the future. When #AC exception for split lock is triggered from user process, the process is killed by SIGBUS. To execute the process properly, user application developer needs to fix the split lock issue. When #AC exception for split lock is triggered from a kernel instruction, disable #AC for split lock on local CPU and warn the split lock issue. After the exception, the faulting instruction will be executed and kernel execution continues. #AC for split lock is only disabled on the local CPU not globally. It will be re-enabled if the CPU is offline and then online. Kernel developer should check the warning, which contains helpful faulting address, context, and callstack info, and fix the split lock issue one by one. Then further split lock may be captured and fixed. After bit 29 in MSR_TEST_CTL is set as one in kernel, firmware inherits the setting when firmware is executed in S4, S5, run time services, SMI, etc. Split lock issue in firmware triggers #AC and may hang the system depending on how firmware handles the #AC. It's up to firmware developer to fix the split lock issues in firmware. Signed-off-by: Fenghua Yu <fenghua.yu@intel.com> --- arch/x86/kernel/traps.c | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+)