From: David Woodhouse dwmw@amazon.co.uk
commit fcb732d8f8cf6084f8480015ad41d25fb023a4dd upstream.
There are circumstances whem kvm_xen_update_runstate_guest() should not sleep because it ends up being called from __schedule() when the vCPU is preempted:
[ 222.830825] kvm_xen_update_runstate_guest+0x24/0x100 [ 222.830878] kvm_arch_vcpu_put+0x14c/0x200 [ 222.830920] kvm_sched_out+0x30/0x40 [ 222.830960] __schedule+0x55c/0x9f0
To handle this, make it use the same trick as __kvm_xen_has_interrupt(), of using the hva from the gfn_to_hva_cache directly. Then it can use pagefault_disable() around the accesses and just bail out if the page is absent (which is unlikely).
I almost switched to using a gfn_to_pfn_cache here and bailing out if kvm_map_gfn() fails, like kvm_steal_time_set_preempted() does — but on closer inspection it looks like kvm_map_gfn() will *always* fail in atomic context for a page in IOMEM, which means it will silently fail to make the update every single time for such guests, AFAICT. So I didn't do it that way after all. And will probably fix that one too.
Cc: stable@vger.kernel.org Fixes: 30b5c851af79 ("KVM: x86/xen: Add support for vCPU runstate information") Signed-off-by: David Woodhouse dwmw@amazon.co.uk Message-Id: b17a93e5ff4561e57b1238e3e7ccd0b613eb827e.camel@infradead.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/xen.c | 97 ++++++++++++++++++++++++++++++++++++----------------- 1 file changed, 67 insertions(+), 30 deletions(-)
--- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -93,32 +93,57 @@ static void kvm_xen_update_runstate(stru void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, int state) { struct kvm_vcpu_xen *vx = &v->arch.xen; + struct gfn_to_hva_cache *ghc = &vx->runstate_cache; + struct kvm_memslots *slots = kvm_memslots(v->kvm); + bool atomic = (state == RUNSTATE_runnable); uint64_t state_entry_time; - unsigned int offset; + int __user *user_state; + uint64_t __user *user_times;
kvm_xen_update_runstate(v, state);
if (!vx->runstate_set) return;
- BUILD_BUG_ON(sizeof(struct compat_vcpu_runstate_info) != 0x2c); + if (unlikely(slots->generation != ghc->generation || kvm_is_error_hva(ghc->hva)) && + kvm_gfn_to_hva_cache_init(v->kvm, ghc, ghc->gpa, ghc->len)) + return; + + /* We made sure it fits in a single page */ + BUG_ON(!ghc->memslot); + + if (atomic) + pagefault_disable();
- offset = offsetof(struct compat_vcpu_runstate_info, state_entry_time); -#ifdef CONFIG_X86_64 /* - * The only difference is alignment of uint64_t in 32-bit. - * So the first field 'state' is accessed directly using - * offsetof() (where its offset happens to be zero), while the - * remaining fields which are all uint64_t, start at 'offset' - * which we tweak here by adding 4. + * The only difference between 32-bit and 64-bit versions of the + * runstate struct us the alignment of uint64_t in 32-bit, which + * means that the 64-bit version has an additional 4 bytes of + * padding after the first field 'state'. + * + * So we use 'int __user *user_state' to point to the state field, + * and 'uint64_t __user *user_times' for runstate_entry_time. So + * the actual array of time[] in each state starts at user_times[1]. */ + BUILD_BUG_ON(offsetof(struct vcpu_runstate_info, state) != 0); + BUILD_BUG_ON(offsetof(struct compat_vcpu_runstate_info, state) != 0); + user_state = (int __user *)ghc->hva; + + BUILD_BUG_ON(sizeof(struct compat_vcpu_runstate_info) != 0x2c); + + user_times = (uint64_t __user *)(ghc->hva + + offsetof(struct compat_vcpu_runstate_info, + state_entry_time)); +#ifdef CONFIG_X86_64 BUILD_BUG_ON(offsetof(struct vcpu_runstate_info, state_entry_time) != offsetof(struct compat_vcpu_runstate_info, state_entry_time) + 4); BUILD_BUG_ON(offsetof(struct vcpu_runstate_info, time) != offsetof(struct compat_vcpu_runstate_info, time) + 4);
if (v->kvm->arch.xen.long_mode) - offset = offsetof(struct vcpu_runstate_info, state_entry_time); + user_times = (uint64_t __user *)(ghc->hva + + offsetof(struct vcpu_runstate_info, + state_entry_time)); #endif /* * First write the updated state_entry_time at the appropriate @@ -132,10 +157,8 @@ void kvm_xen_update_runstate_guest(struc BUILD_BUG_ON(sizeof(((struct compat_vcpu_runstate_info *)0)->state_entry_time) != sizeof(state_entry_time));
- if (kvm_write_guest_offset_cached(v->kvm, &v->arch.xen.runstate_cache, - &state_entry_time, offset, - sizeof(state_entry_time))) - return; + if (__put_user(state_entry_time, user_times)) + goto out; smp_wmb();
/* @@ -149,11 +172,8 @@ void kvm_xen_update_runstate_guest(struc BUILD_BUG_ON(sizeof(((struct compat_vcpu_runstate_info *)0)->state) != sizeof(vx->current_runstate));
- if (kvm_write_guest_offset_cached(v->kvm, &v->arch.xen.runstate_cache, - &vx->current_runstate, - offsetof(struct vcpu_runstate_info, state), - sizeof(vx->current_runstate))) - return; + if (__put_user(vx->current_runstate, user_state)) + goto out;
/* * Write the actual runstate times immediately after the @@ -168,24 +188,23 @@ void kvm_xen_update_runstate_guest(struc BUILD_BUG_ON(sizeof(((struct vcpu_runstate_info *)0)->time) != sizeof(vx->runstate_times));
- if (kvm_write_guest_offset_cached(v->kvm, &v->arch.xen.runstate_cache, - &vx->runstate_times[0], - offset + sizeof(u64), - sizeof(vx->runstate_times))) - return; - + if (__copy_to_user(user_times + 1, vx->runstate_times, sizeof(vx->runstate_times))) + goto out; smp_wmb();
/* * Finally, clear the XEN_RUNSTATE_UPDATE bit in the guest's * runstate_entry_time field. */ - state_entry_time &= ~XEN_RUNSTATE_UPDATE; - if (kvm_write_guest_offset_cached(v->kvm, &v->arch.xen.runstate_cache, - &state_entry_time, offset, - sizeof(state_entry_time))) - return; + __put_user(state_entry_time, user_times); + smp_wmb(); + + out: + mark_page_dirty_in_slot(v->kvm, ghc->memslot, ghc->gpa >> PAGE_SHIFT); + + if (atomic) + pagefault_enable(); }
int __kvm_xen_has_interrupt(struct kvm_vcpu *v) @@ -337,6 +356,12 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcp break; }
+ /* It must fit within a single page */ + if ((data->u.gpa & ~PAGE_MASK) + sizeof(struct vcpu_info) > PAGE_SIZE) { + r = -EINVAL; + break; + } + r = kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.xen.vcpu_info_cache, data->u.gpa, @@ -354,6 +379,12 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcp break; }
+ /* It must fit within a single page */ + if ((data->u.gpa & ~PAGE_MASK) + sizeof(struct pvclock_vcpu_time_info) > PAGE_SIZE) { + r = -EINVAL; + break; + } + r = kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.xen.vcpu_time_info_cache, data->u.gpa, @@ -375,6 +406,12 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcp break; }
+ /* It must fit within a single page */ + if ((data->u.gpa & ~PAGE_MASK) + sizeof(struct vcpu_runstate_info) > PAGE_SIZE) { + r = -EINVAL; + break; + } + r = kvm_gfn_to_hva_cache_init(vcpu->kvm, &vcpu->arch.xen.runstate_cache, data->u.gpa,