* tip-bot for Peter Zijlstra (a.p.zijlstra@xxxxxxxxx) wrote: > Commit-ID: 74193ef0ecab92535c8517f082f1f50504526c9b > Gitweb: http://git.kernel.org/tip/74193ef0ecab92535c8517f082f1f50504526c9b > Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > AuthorDate: Mon, 15 Jun 2009 13:07:24 +0200 > Committer: Ingo Molnar <mingo@xxxxxxx> > CommitDate: Mon, 15 Jun 2009 15:57:53 +0200 > > perf_counter: x86: Fix call-chain support to use NMI-safe methods > > __copy_from_user_inatomic() isn't NMI safe in that it can trigger > the page fault handler which is another trap and its return path > invokes IRET which will also close the NMI context. > > Therefore use a GUP based approach to copy the stack frames over. > > We tried an alternative solution as well: we used a forward ported > version of Mathieu Desnoyers's "NMI safe INT3 and Page Fault" patch > that modifies the exception return path to use an open-coded IRET with > explicit stack unrolling and TF checking. > > This didnt work as it interacted with faulting user-space instructions, > causing them not to restart properly, which corrupts user-space > registers. > > Solving that would probably involve disassembling those instructions > and backtracing the RIP. But even without that, the code was deemed > rather complex to the already non-trivial x86 entry assembly code, > so instead we went for this GUP based method that does a > software-walk of the pagetables. > Hrm, I'm probably missing something. Normally, you should test for "in_nmi()" upon return from exception, and only in these cases go for the open-coded IRET with stack unrolling and ret. I really don't see how you end up messing up the page fault return to userspace path, as it's impossible to have in_nmi() set. Mathieu > Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> > Cc: Nick Piggin <npiggin@xxxxxxx> > Cc: Pekka Enberg <penberg@xxxxxxxxxxxxxx> > Cc: Vegard Nossum <vegard.nossum@xxxxxxxxx> > Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx> > Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Cc: Mike Galbraith <efault@xxxxxx> > Cc: Paul Mackerras <paulus@xxxxxxxxx> > Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> > LKML-Reference: <new-submission> > Signed-off-by: Ingo Molnar <mingo@xxxxxxx> > > > --- > arch/x86/kernel/cpu/perf_counter.c | 49 ++++++++++++++++++++++++++++------- > 1 files changed, 39 insertions(+), 10 deletions(-) > > diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c > index 6d5e7cf..e8c68a5 100644 > --- a/arch/x86/kernel/cpu/perf_counter.c > +++ b/arch/x86/kernel/cpu/perf_counter.c > @@ -19,6 +19,7 @@ > #include <linux/kdebug.h> > #include <linux/sched.h> > #include <linux/uaccess.h> > +#include <linux/highmem.h> > > #include <asm/apic.h> > #include <asm/stacktrace.h> > @@ -1617,20 +1618,48 @@ perf_callchain_kernel(struct pt_regs *regs, struct perf_callchain_entry *entry) > entry->kernel = entry->nr - nr; > } > > -static int copy_stack_frame(const void __user *fp, struct stack_frame *frame) > +/* > + * best effort, GUP based copy_from_user() that assumes IRQ or NMI context > + */ > +static unsigned long > +copy_from_user_nmi(void *to, const void __user *from, unsigned long n) > { > + unsigned long offset, addr = (unsigned long)from; > + int type = in_nmi() ? KM_NMI : KM_IRQ0; > + unsigned long size, len = 0; > + struct page *page; > + void *map; > int ret; > > - if (!access_ok(VERIFY_READ, fp, sizeof(*frame))) > - return 0; > + do { > + ret = __get_user_pages_fast(addr, 1, 0, &page); > + if (!ret) > + break; > > - ret = 1; > - pagefault_disable(); > - if (__copy_from_user_inatomic(frame, fp, sizeof(*frame))) > - ret = 0; > - pagefault_enable(); > + offset = addr & (PAGE_SIZE - 1); > + size = min(PAGE_SIZE - offset, n - len); > > - return ret; > + map = kmap_atomic(page, type); > + memcpy(to, map+offset, size); > + kunmap_atomic(map, type); > + put_page(page); > + > + len += size; > + to += size; > + addr += size; > + > + } while (len < n); > + > + return len; > +} > + > +static int copy_stack_frame(const void __user *fp, struct stack_frame *frame) > +{ > + unsigned long bytes; > + > + bytes = copy_from_user_nmi(frame, fp, sizeof(*frame)); > + > + return bytes == sizeof(*frame); > } > > static void > @@ -1643,7 +1672,7 @@ perf_callchain_user(struct pt_regs *regs, struct perf_callchain_entry *entry) > if (!user_mode(regs)) > regs = task_pt_regs(current); > > - fp = (void __user *)regs->bp; > + fp = (void __user *)regs->bp; > > callchain_store(entry, regs->ip); > -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- 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