Final question: are any of these done in frequent paths? (I believe no, but...)
Dave Hansen <[email protected]> wrote: > >In short, it is illegal to call __pa() on an address holding >a percpu variable. The times when this actually matters are >pretty obscure (certain 32-bit NUMA systems), but it _does_ >happen. It is important to keep KVM guests working on these >systems because the real hardware is getting harder and >harder to find. > >This bug manifested first by me seeing a plain hang at boot >after this message: > > CPU 0 irqstacks, hard=f3018000 soft=f301a000 > >or, sometimes, it would actually make it out to the console: > >[ 0.000000] BUG: unable to handle kernel paging request at ffffffff > >I eventually traced it down to the KVM async pagefault code. >This can be worked around by disabling that code either at >compile-time, or on the kernel command-line. > >The kvm async pagefault code was injecting page faults in >to the guest which the guest misinterpreted because its >"reason" was not being properly sent from the host. > >The guest passes a physical address of an per-cpu async page >fault structure via an MSR to the host. Since __pa() is >broken on percpu data, the physical address it sent was >bascially bogus and the host went scribbling on random data. >The guest never saw the real reason for the page fault (it >was injected by the host), assumed that the kernel had taken >a _real_ page fault, and panic()'d. The behavior varied, >though, depending on what got corrupted by the bad write. > >Signed-off-by: Dave Hansen <[email protected]> >Acked-by: Rik van Riel <[email protected]> >--- > > linux-2.6.git-dave/arch/x86/kernel/kvm.c | 9 +++++---- > linux-2.6.git-dave/arch/x86/kernel/kvmclock.c | 4 ++-- > 2 files changed, 7 insertions(+), 6 deletions(-) > >diff -puN arch/x86/kernel/kvm.c~fix-kvm-__pa-use-on-percpu-areas >arch/x86/kernel/kvm.c >--- >linux-2.6.git/arch/x86/kernel/kvm.c~fix-kvm-__pa-use-on-percpu-areas >2013-01-17 >10:22:26.914436992 -0800 >+++ linux-2.6.git-dave/arch/x86/kernel/kvm.c 2013-01-17 >10:22:26.922437062 -0800 >@@ -289,9 +289,9 @@ static void kvm_register_steal_time(void > > memset(st, 0, sizeof(*st)); > >- wrmsrl(MSR_KVM_STEAL_TIME, (__pa(st) | KVM_MSR_ENABLED)); >+ wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | >KVM_MSR_ENABLED)); > printk(KERN_INFO "kvm-stealtime: cpu %d, msr %lx\n", >- cpu, __pa(st)); >+ cpu, slow_virt_to_phys(st)); > } > >static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) = >KVM_PV_EOI_DISABLED; >@@ -316,7 +316,7 @@ void __cpuinit kvm_guest_cpu_init(void) > return; > > if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF) && kvmapf) { >- u64 pa = __pa(&__get_cpu_var(apf_reason)); >+ u64 pa = slow_virt_to_phys(&__get_cpu_var(apf_reason)); > > #ifdef CONFIG_PREEMPT > pa |= KVM_ASYNC_PF_SEND_ALWAYS; >@@ -332,7 +332,8 @@ void __cpuinit kvm_guest_cpu_init(void) > /* Size alignment is implied but just to make it explicit. */ > BUILD_BUG_ON(__alignof__(kvm_apic_eoi) < 4); > __get_cpu_var(kvm_apic_eoi) = 0; >- pa = __pa(&__get_cpu_var(kvm_apic_eoi)) | KVM_MSR_ENABLED; >+ pa = slow_virt_to_phys(&__get_cpu_var(kvm_apic_eoi)) >+ | KVM_MSR_ENABLED; > wrmsrl(MSR_KVM_PV_EOI_EN, pa); > } > >diff -puN arch/x86/kernel/kvmclock.c~fix-kvm-__pa-use-on-percpu-areas >arch/x86/kernel/kvmclock.c >--- >linux-2.6.git/arch/x86/kernel/kvmclock.c~fix-kvm-__pa-use-on-percpu-areas >2013-01-17 >10:22:26.918437028 -0800 >+++ linux-2.6.git-dave/arch/x86/kernel/kvmclock.c 2013-01-17 >10:22:26.922437062 -0800 >@@ -162,8 +162,8 @@ int kvm_register_clock(char *txt) > int low, high, ret; > struct pvclock_vcpu_time_info *src = &hv_clock[cpu].pvti; > >- low = (int)__pa(src) | 1; >- high = ((u64)__pa(src) >> 32); >+ low = (int)slow_virt_to_phys(src) | 1; >+ high = ((u64)slow_virt_to_phys(src) >> 32); > ret = native_write_msr_safe(msr_kvm_system_time, low, high); > printk(KERN_INFO "kvm-clock: cpu %d, msr %x:%x, %s\n", > cpu, high, low, txt); >_ -- Sent from my mobile phone. Please excuse brevity and lack of formatting. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
