Re: [PATCH 2/4] KVM: PPC: Book3S HV: Map single pages when doing dirty page logging

[Suraj Jitindar Singh <sjitindarsingh@gmail.com>]

On Wed, 2018-12-12 at 15:16 +1100, Paul Mackerras wrote:
> For radix guests, this makes KVM map guest memory as individual pages
> when dirty page logging is enabled for the memslot corresponding to
> the
> guest real address.  Having a separate partition-scoped PTE for each
> system page mapped to the guest means that we have a separate dirty
> bit for each page, thus making the reported dirty bitmap more
> accurate.
> Without this, if part of guest memory is backed by transparent huge
> pages, the dirty status is reported at a 2MB granularity rather than
> a 64kB (or 4kB) granularity for that part, causing userspace to have
> to transmit more data when migrating the guest.

Reviewed-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>

> 
> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
> ---
>  arch/powerpc/kvm/book3s_64_mmu_radix.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c
> b/arch/powerpc/kvm/book3s_64_mmu_radix.c
> index d68162e..87ad35e 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
> @@ -683,6 +683,7 @@ int kvmppc_book3s_instantiate_page(struct
> kvm_vcpu *vcpu,
>  	pte_t pte, *ptep;
>  	unsigned int shift, level;
>  	int ret;
> +	bool large_enable;
>  
>  	/* used to check for invalidations in progress */
>  	mmu_seq = kvm->mmu_notifier_seq;
> @@ -732,12 +733,15 @@ int kvmppc_book3s_instantiate_page(struct
> kvm_vcpu *vcpu,
>  	pte = *ptep;
>  	local_irq_enable();
>  
> +	/* If we're logging dirty pages, always map single pages */
> +	large_enable = !(memslot->flags & KVM_MEM_LOG_DIRTY_PAGES);
> +
>  	/* Get pte level from shift/size */
> -	if (shift = PUD_SHIFT &&
> +	if (large_enable && shift = PUD_SHIFT &&
>  	    (gpa & (PUD_SIZE - PAGE_SIZE)) =
>  	    (hva & (PUD_SIZE - PAGE_SIZE))) {
>  		level = 2;
> -	} else if (shift = PMD_SHIFT &&
> +	} else if (large_enable && shift = PMD_SHIFT &&
>  		   (gpa & (PMD_SIZE - PAGE_SIZE)) =
>  		   (hva & (PMD_SIZE - PAGE_SIZE))) {
>  		level = 1;