Message ID | 1367137941-4310-4-git-send-email-jordan.l.justen@intel.com |
---|---|
State | New |
Headers | show |
On 2013-04-28 10:32, Jordan Justen wrote: > On a Linux 3.8.0 based kernel, I occasionally saw a situation > where the memory region would continue to trap on memory > read even though KVM_MEM_READONLY was set. Only 3.8.0? Did you bisect the issue down to the causing commit? Is it fixed in later versions? Jan > > I found that if I set the slot to a size of 0, and before > setting the slot, it would then behave as expected. > > Signed-off-by: Jordan Justen <jordan.l.justen@intel.com> > Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> > --- > kvm-all.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kvm-all.c b/kvm-all.c > index 95e6bf2..e2ddbcb 100644 > --- a/kvm-all.c > +++ b/kvm-all.c > @@ -205,6 +205,13 @@ static int kvm_set_user_memory_region(KVMState *s, KVMSlot *slot) > if (s->migration_log) { > mem.flags |= KVM_MEM_LOG_DIRTY_PAGES; > } > + if (mem.flags & KVM_MEM_READONLY && mem.memory_size != 0) { > + /* Workaround an issue with setting a READONLY slot. Set the > + * slot size to 0 before setting the slot to the desired value. */ > + mem.memory_size = 0; > + kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem); > + mem.memory_size = slot->memory_size; > + } > return kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem); > } > >
On Mon, Apr 29, 2013 at 3:29 AM, Jan Kiszka <jan.kiszka@siemens.com> wrote: > On 2013-04-28 10:32, Jordan Justen wrote: >> On a Linux 3.8.0 based kernel, I occasionally saw a situation >> where the memory region would continue to trap on memory >> read even though KVM_MEM_READONLY was set. > > Only 3.8.0? Did you bisect the issue down to the causing commit? Is it > fixed in later versions? I'm sorry, I have not tried to bisect, nor have I tried a newer kernel version. Speculating a bit, it seems that a trap to the region might cause the issue. This is what happens in the failing case: * Disable mem region * Trap on access to region * Enable readonly region * Next read access will trap when it shouldn't Here is the what happen with the work-around: * Disable mem region * Trap on access to region * (Re-)disable mem region (work-around adds this) * Enable readonly region * Next read access will not trap (proper behavior) -Jordan
On 04/28/2013 04:32 PM, Jordan Justen wrote: > On a Linux 3.8.0 based kernel, I occasionally saw a situation > where the memory region would continue to trap on memory > read even though KVM_MEM_READONLY was set. > > I found that if I set the slot to a size of 0, and before > setting the slot, it would then behave as expected. Yes, the KVM_MEM_READONLY flag can not be directly changed, see the commit 75d61fbcf563373696578570e914f555e12c8d97 on kvm tree. Do you think the way which deletes the memslot before changing the KVM_MEM_READONLY hurts the performance? If yes, i will make it be directly changed. Thanks for you implementing the READONLY memory in Qemu. Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
diff --git a/kvm-all.c b/kvm-all.c index 95e6bf2..e2ddbcb 100644 --- a/kvm-all.c +++ b/kvm-all.c @@ -205,6 +205,13 @@ static int kvm_set_user_memory_region(KVMState *s, KVMSlot *slot) if (s->migration_log) { mem.flags |= KVM_MEM_LOG_DIRTY_PAGES; } + if (mem.flags & KVM_MEM_READONLY && mem.memory_size != 0) { + /* Workaround an issue with setting a READONLY slot. Set the + * slot size to 0 before setting the slot to the desired value. */ + mem.memory_size = 0; + kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem); + mem.memory_size = slot->memory_size; + } return kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem); }
On a Linux 3.8.0 based kernel, I occasionally saw a situation where the memory region would continue to trap on memory read even though KVM_MEM_READONLY was set. I found that if I set the slot to a size of 0, and before setting the slot, it would then behave as expected. Signed-off-by: Jordan Justen <jordan.l.justen@intel.com> Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> --- kvm-all.c | 7 +++++++ 1 file changed, 7 insertions(+)