Re: [PATCH v8 2/3] KVM: x86: Dirty quota-based throttling of vcpus

[Shivam Kumar <shivam.kumar1@nutanix.com>]

On 28/02/23 7:01 am, Yuan Yao wrote:
> On Sat, Feb 25, 2023 at 08:47:59PM +0000, Shivam Kumar wrote:
>> Call update_dirty_quota whenever a page is marked dirty with
>> appropriate arch-specific page size. Process the KVM request
>> KVM_REQ_DIRTY_QUOTA_EXIT (raised by update_dirty_quota) to exit to
>> userspace with exit reason KVM_EXIT_DIRTY_QUOTA_EXHAUSTED.
>>
>> Suggested-by: Shaju Abraham <shaju.abraham@nutanix.com>
>> Suggested-by: Manish Mishra <manish.mishra@nutanix.com>
>> Co-developed-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
>> Signed-off-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
>> Signed-off-by: Shivam Kumar <shivam.kumar1@nutanix.com>
>> ---
>>   arch/x86/kvm/Kconfig       |  1 +
>>   arch/x86/kvm/mmu/mmu.c     |  8 +++++++-
>>   arch/x86/kvm/mmu/spte.c    |  3 +++
>>   arch/x86/kvm/mmu/tdp_mmu.c |  3 +++
>>   arch/x86/kvm/vmx/vmx.c     |  5 +++++
>>   arch/x86/kvm/x86.c         | 16 ++++++++++++++++
>>   arch/x86/kvm/xen.c         | 12 +++++++++++-
>>   7 files changed, 46 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
>> index 8e578311ca9d..8621a9512572 100644
>> --- a/arch/x86/kvm/Kconfig
>> +++ b/arch/x86/kvm/Kconfig
>> @@ -48,6 +48,7 @@ config KVM
>>   	select KVM_VFIO
>>   	select SRCU
>>   	select INTERVAL_TREE
>> +	select HAVE_KVM_DIRTY_QUOTA
>>   	select HAVE_KVM_PM_NOTIFIER if PM
>>   	select KVM_GENERIC_HARDWARE_ENABLING
>>   	help
>> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
>> index c8ebe542c565..e0c8348ecdf1 100644
>> --- a/arch/x86/kvm/mmu/mmu.c
>> +++ b/arch/x86/kvm/mmu/mmu.c
>> @@ -3323,8 +3323,14 @@ fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
>>   	if (!try_cmpxchg64(sptep, &old_spte, new_spte))
>>   		return false;
>>
>> -	if (is_writable_pte(new_spte) && !is_writable_pte(old_spte))
>> +	if (is_writable_pte(new_spte) && !is_writable_pte(old_spte)) {
>> +#ifdef CONFIG_HAVE_KVM_DIRTY_QUOTA
>> +		struct kvm_mmu_page *sp = sptep_to_sp(sptep);
>> +
>> +		update_dirty_quota(vcpu->kvm, (1L << SPTE_LEVEL_SHIFT(sp->role.level)));
>> +#endif
>>   		mark_page_dirty_in_slot(vcpu->kvm, fault->slot, fault->gfn);
> 
> Possible to call update_dirty_quota() from mark_page_dirty_in_slot() ?
> Then other Architectures can be covered yet.

As Marc commented on the first patch of this patchset, 
mark_page_dirty_in_slot can be called multiple times for the same page, 
e.g. in the case of PML for nested guests. If bitmap-based dirty 
tracking is not enabled, we might not be able to handle those cases 
without adding an extra param (which can tell us whether a dirty quota 
update is required or not) in mark_page_dirty_in_slot. Thanks.

Thanks,
Shivam