On Mon, Jan 25, 2021 at 10:10:44PM +0800, Yanan Wang wrote:
> After dirty-logging is stopped for a VM configured with huge mappings,
> KVM will recover the table mappings back to block mappings. As we only
> replace the existing page tables with a block entry and the cacheability
> has not been changed, the cache maintenance opreations can be skipped.
>
> Signed-off-by: Yanan Wang <wangyanan55@xxxxxxxxxx>
> ---
> arch/arm64/kvm/mmu.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 8e8549ea1d70..37b427dcbc4f 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -744,7 +744,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> {
> int ret = 0;
> bool write_fault, writable, force_pte = false;
> - bool exec_fault;
> + bool exec_fault, adjust_hugepage;
> bool device = false;
> unsigned long mmu_seq;
> struct kvm *kvm = vcpu->kvm;
> @@ -872,12 +872,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> mark_page_dirty(kvm, gfn);
> }
>
> - if (fault_status != FSC_PERM && !device)
> + /*
> + * There is no necessity to perform cache maintenance operations if we
> + * will only replace the existing table mappings with a block mapping.
> + */
> + adjust_hugepage = fault_granule < vma_pagesize ? true : false;
nit: you don't need the '? true : false' part
That said, your previous patch checks for 'fault_granule > vma_pagesize',
so I'm not sure the local variable helps all that much here because it
obscures the size checks in my opinion. It would be more straight-forward
if we could structure the logic as:
if (fault_granule < vma_pagesize) {
} else if (fault_granule > vma_page_size) {
} else {
}
With some comments describing what we can infer about the memcache and cache
maintenance requirements for each case.
Will
