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

Christoffer Dall
2014-06-11T07:03:57Z

On Tue, Jun 10, 2014 at 11:08:24AM -0700, Mario Smarduch wrote:
> On 06/10/2014 02:22 AM, Christoffer Dall wrote:
> > On Mon, Jun 09, 2014 at 06:47:12PM -0700, Mario Smarduch wrote:
> >> On 06/08/2014 05:05 AM, Christoffer Dall wrote:
> >>> On Fri, Jun 06, 2014 at 10:33:41AM -0700, Mario Smarduch wrote:
> >>>> kvm_vm_ioctl_get_dirty_log() is generic used by x86, ARM. x86 recent patch
> >>>> changed this function, this patch picks up those changes, re-tested everything
> >>>> works. Applies cleanly with other patches.
> >>>>
> >>>> This patch adds support for keeping track of VM dirty pages. As dirty page log
> >>>> is retrieved, the pages that have been written are write protected again for
> >>>> next write and log read.
> >>>>
> >>>> Signed-off-by: Mario Smarduch <m.smarduch@samsung.com>
> >>>> ---
> >>>> arch/arm/include/asm/kvm_host.h | 3 ++
> >>>> arch/arm/kvm/arm.c | 5 ---
> >>>> arch/arm/kvm/mmu.c | 79 +++++++++++++++++++++++++++++++++++
> >>>> arch/x86/kvm/x86.c | 86 ---------------------------------------
> >>>> virt/kvm/kvm_main.c | 86 +++++++++++++++++++++++++++++++++++++++
> >>>> 5 files changed, 168 insertions(+), 91 deletions(-)
> >>>>
> >>>> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> >>>> index 59565f5..b760f9c 100644
> >>>> --- a/arch/arm/include/asm/kvm_host.h
> >>>> +++ b/arch/arm/include/asm/kvm_host.h
> >>>> @@ -232,5 +232,8 @@ u64 kvm_arm_timer_get_reg(struct kvm_vcpu *, u64 regid);
> >>>> int kvm_arm_timer_set_reg(struct kvm_vcpu *, u64 regid, u64 value);
> >>>>
> >>>> void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
> >>>> +void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
> >>>> + struct kvm_memory_slot *slot,
> >>>> + gfn_t gfn_offset, unsigned long mask);
> >>>
> >>> Do all other architectures implement this function? arm64?
> >>
> >> Besides arm, x86 but the function is not generic.
> >>>
> >
> > you're now calling this from generic code, so all architecture must
> > implement it, and the prototype should proably be in
> > include/linux/kvm_host.h, not in the arch-specific headers.
> Ah ok.
> >
> >>>>
> >>>> #endif /* __ARM_KVM_HOST_H__ */
> >>>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> >>>> index dfd63ac..f06fb21 100644
> >>>> --- a/arch/arm/kvm/arm.c
> >>>> +++ b/arch/arm/kvm/arm.c
> >>>> @@ -780,11 +780,6 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> >>>> }
> >>>> }
> >>>>
> >>>> -int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log)
> >>>> -{
> >>>> - return -EINVAL;
> >>>> -}
> >>>> -
> >>>
> >>> What about the other architectures implementing this function?
> >>
> >> Six architectures define this function. With this patch this
> >> function is generic in kvm_main.c used by x86.
> >
> > But you're not defining it as a weak symbol (and I don't suspect that
> > you should unless other archs do this in a *very* different way), so you
> > need to either remove it from the other archs, make it a weak symbol (I
> > hope this is not the case) or do something else.
> Mistake on my part I just cut and paste Xiaos x86's recent upstream patch and
> didn't add weak definition.
>
> I looked at IA64, MIPS (two of them ), S390 somewhat similar but quite
> different implementations. They use a sync version, where the dirty bitmaps
> are maintained at arch level and then copied to memslot->dirty_bitmap. There
> is only commonality between x86 and ARM right now, x86 uses
> memslot->dirty_bitmap directly.
>
> Maybe this function should go back to architecture layer, it's
> unlikely it can become generic across all architectures.
>
> 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