Re: [RESEND PATCH v7 3/4] arm: dirty log write protect management support

Mario Smarduch
2014-07-17T16:18:04Z

Hi Christoffer,
Just back from holiday - a short plan to resume work.

- move VM tlb flush and kvm log functions to generic, per Paolo's
comments use Kconfig approach
- update other architectures make sure they compile
- Keep it ARMv7 for now

Get maintainers to test the branch.

In parallel add dirty log support to ARMv8, to test I would
add a QEMU monitor function to validate general operation.

Your thoughts?

Thanks,
Mario

On 07/03/2014 08:04 AM, Christoffer Dall wrote:
> On Tue, Jun 17, 2014 at 06:41:52PM -0700, Mario Smarduch wrote:
>> On 06/11/2014 12:03 AM, Christoffer Dall wrote:
>>
>>>>
>>>> There is also the issue of kvm_flush_remote_tlbs(), that's also weak,
>>>> the generic one is using IPIs. Since it's only used in mmu.c maybe make
>>>> this one static.
>>>>
>>> So I don't see a lot of use of weak symbols in kvm_main.c (actually on
>>> kvmarm/next I don't see any), but we do want to share code when more
>>> than one architecture implements something in the exact same way, like
>>> it seems x86 and ARM is doing here for this particular function.
>>>
>>> I think the KVM scheme is usually to check for some define, like:
>>>
>>> #ifdef KVM_ARCH_HAVE_GET_DIRTY_LOG
>>> ret = kvm_arch_get_dirty_log(...);
>>> #else
>>> ret = kvm_get_dirty_log(...);
>>> #endif
>>>
>>> but Paolo may have a more informed oppinion of how to deal with these.
>>>
>>> Thanks,
>>> -Christoffer
>>>
>>
>>
>> One approach I'm trying looking at the code in kvm_main().
>> This approach applies more to selecting features as opposed to
>> selecting generic vs architecture specific functions.
>>
>> 1.-------------------------------------------------
>> - add to 'virt/kvm/Kconfig'
>> config HAVE_KVM_ARCH_TLB_FLUSH_ALL
>> bool
>>
>> config HAVE_KVM_ARCH_DIRTY_LOG
>> bool
>> 2.--------------------------------------------------
>> For ARM and later ARM64 add to 'arch/arm[64]/kvm/Kconfig'
>> config KVM
>> bool "Kernel-based Virtual Machine (KVM) support"
>> ...
>> select HAVE_KVM_ARCH_TLB_FLUSH_ALL
>> ..
>>
>> Not for HAVE_KVM_ARCH_DIRTY_LOG given it's shared with x86,
>> but would need to do it for every other architecture that
>> does not share it (except initially for arm64 since it
>> will use the variant that returns -EINVAL until feature
>> is supported)
>>
>> 3------------------------------------------------------
>> In kvm_main.c would have something like
>>
>> void kvm_flush_remote_tlbs(struct kvm *kvm)
>> {
>> #ifdef CONFIG_HAVE_KVM_ARCH_TLB_FLUSH_ALL
>> kvm_arch_flush_remote_tlbs(kvm);
>> #else
>> long dirty_count = kvm->tlbs_dirty;
>>
>> smp_mb();
>> if (make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH))
>> ++kvm->stat.remote_tlb_flush;
>> cmpxchg(&kvm->tlbs_dirty, dirty_count, 0);
>> #endif
>> }
>>
>> Then add void kvm_flush_remote_tlbs(struct kvm *kvm) definition
>> to arm kvm_host.h. Define the function in this case mmu.c
>>
>> For the dirty log function
>> int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
>> struct kvm_dirty_log *log)
>> {
>> #ifdef CONFIG_HAVE_KVM_ARCH_DIRTY_LOG
>> kvm_arch_vm_ioctl_get_dirty_log(kvm, log);
>> #else
>> int r;
>> struct kvm_memory_slot *memslot;
>> unsigned long n, i;
>> unsigned long *dirty_bitmap;
>> unsigned long *dirty_bitmap_buffer;
>> bool is_dirty = false;
>> ...
>>
>> But then you have to go into every architecture and define the
>> kvm_arch_vm_...() variant.
>>
>> Is this the right way to go? Or is there a simpler way?
>>
> Hmmm, I'm really not an expert in the 'established procedures' for what
> to put in config files etc., but here's my basic take:
>
> a) you wouldn't put a config option in Kconfig unless it's comething
> that's actually configurable or some generic feature/subsystem that
> should only be enabled if hardware has certain capabilities or other
> config options enabled.
>
> b) this seems entirely an implementation issue and not depending on
> anything users should select.
>
> c) therefore, I think it's either a question of always having an
> arch-specific implementation that you probe for its return value or you
> have some sort of define in the header files for the
> arch/X/include/asm/kvm_host.h to control what you need.
>
> -Christoffer
>