[PATCH v14 3/7] KVM: x86: switch to kvm_get_dirty_log_protect

[Mario Smarduch]

Hi Paolo,
   I took a closer look at Christoffers comment,
the _log description in x86.c is a repeat of the
_protect description in kvm_main.c.

I'm wondering if description below would be acceptable, or
perhaps you had a reason leaving it as is.

For the ARM variant I would word same. Please advise.

Thanks.

"
/**
 * kvm_vm_ioctl_get_dirty_log - get and clear the log of dirty pages in
a slot
 * @kvm: kvm instance
 * @log: slot id and address to which we copy the log
 *
 * Steps 1-4 below provide general overview of dirty page logging. See
 * kvm_get_dirty_log_protect() function description for additional details.
 *
 * We call kvm_get_dirty_log_protect() to handle steps 1-3, upon return we
 * always flush the TLB (step 4) even if 'protect' failed and dirty bitmap
 * may be corrupt. Regardless of previous outcome KVM logging API does not
 * preclude user space subsequent dirty log read. Flushing TLB insures
writes
 * will be marked dirty for next log read.
 *
 *   1. Take a snapshot of the bit and clear it if needed.
 *   2. Write protect the corresponding page.
 *   3. Copy the snapshot to the userspace.
 *   4. Flush TLB's if needed.
 */
"

On 11/22/2014 11:19 AM, Christoffer Dall wrote:
> On Thu, Nov 13, 2014 at 05:57:44PM -0800, Mario Smarduch wrote:
>> From: Paolo Bonzini <pbonzini at redhat.com>
>>
>> We now have a generic function that does most of the work of
>> kvm_vm_ioctl_get_dirty_log, now use it.
>>
>> Signed-off-by: Mario Smarduch <m.smarduch at samsung.com>
>> ---
>>  arch/x86/include/asm/kvm_host.h |    3 --
>>  arch/x86/kvm/Kconfig            |    1 +
>>  arch/x86/kvm/mmu.c              |    4 +--
>>  arch/x86/kvm/x86.c              |   64 ++++++---------------------------------
>>  4 files changed, 12 insertions(+), 60 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 7c492ed..934dc24 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -805,9 +805,6 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
>>  
>>  void kvm_mmu_reset_context(struct kvm_vcpu *vcpu);
>>  void kvm_mmu_slot_remove_write_access(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);
>>  void kvm_mmu_zap_all(struct kvm *kvm);
>>  void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm);
>>  unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);
>> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
>> index f9d16ff..d073594 100644
>> --- a/arch/x86/kvm/Kconfig
>> +++ b/arch/x86/kvm/Kconfig
>> @@ -39,6 +39,7 @@ config KVM
>>  	select PERF_EVENTS
>>  	select HAVE_KVM_MSI
>>  	select HAVE_KVM_CPU_RELAX_INTERCEPT
>> +	select KVM_GENERIC_DIRTYLOG_READ_PROTECT
>>  	select KVM_VFIO
>>  	---help---
>>  	  Support hosting fully virtualized guest machines using hardware
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index 9314678..bf6b82c 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -1224,7 +1224,7 @@ static bool __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp,
>>  }
>>  
>>  /**
>> - * kvm_mmu_write_protect_pt_masked - write protect selected PT level pages
>> + * kvm_arch_mmu_write_protect_pt_masked - write protect selected PT level pages
>>   * @kvm: kvm instance
>>   * @slot: slot to protect
>>   * @gfn_offset: start of the BITS_PER_LONG pages we care about
>> @@ -1233,7 +1233,7 @@ static bool __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp,
>>   * Used when we do not need to care about huge page mappings: e.g. during dirty
>>   * logging we do not have any such mappings.
>>   */
>> -void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
>> +void kvm_arch_mmu_write_protect_pt_masked(struct kvm *kvm,
>>  				     struct kvm_memory_slot *slot,
>>  				     gfn_t gfn_offset, unsigned long mask)
>>  {
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 8f1e22d..9f8ae9a 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -3606,77 +3606,31 @@ static int kvm_vm_ioctl_reinject(struct kvm *kvm,
>>   *
>>   *   1. Take a snapshot of the bit and clear it if needed.
>>   *   2. Write protect the corresponding page.
>> - *   3. Flush TLB's if needed.
>> - *   4. Copy the snapshot to the userspace.
>> + *   3. Copy the snapshot to the userspace.
>> + *   4. Flush TLB's if needed.
>>   *
>> - * Between 2 and 3, the guest may write to the page using the remaining TLB
>> - * entry.  This is not a problem because the page will be reported dirty at
>> - * step 4 using the snapshot taken before and step 3 ensures that successive
>> - * writes will be logged for the next call.
>> + * Between 2 and 4, the guest may write to the page using the remaining TLB
>> + * entry.  This is not a problem because the page is reported dirty using
>> + * the snapshot taken before and step 4 ensures that writes done after
>> + * exiting to userspace will be logged for the next call.
>>   */
> 
> this seems to duplicate the comment in virt/kvm/kvm_main.c, but
> whatever.
> 
> FWIW:
> Acked-by: Christoffer Dall <christoffer.dall at linaro.org>
>