On Thu, 2015-09-24 at 15:57 +0300, Laurentiu Tudor wrote:
> Book-E MMUv2 present in e6500 cores supports
> powers of 2K page sizes while older MMUv1 cores
> support only powers of 4K page sizes, or in other
> words the LSB of TSIZE on MMUv1 is always 0.
> Thus, on MMUv2 we must not strip the LSB.
We can get better TLB utilization by not stripping it, but why "must not"
which makes it sound like a bugfix rather than an optimization?
> Signed-off-by: Mihai Caraman <mihai.caraman@xxxxxxxxxxxxx>
> [Laurentiu.Tudor@xxxxxxxxxxxxx: addressed review
> feedback, split in distinct patch]
> Signed-off-by: Laurentiu Tudor <Laurentiu.Tudor@xxxxxxxxxxxxx>
> ---
> arch/powerpc/kvm/e500_mmu_host.c | 28 +++++++++++++++++++++-------
> 1 file changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/kvm/e500_mmu_host.c
> b/arch/powerpc/kvm/e500_mmu_host.c
> index 4d33e19..12d5c67 100644
> --- a/arch/powerpc/kvm/e500_mmu_host.c
> +++ b/arch/powerpc/kvm/e500_mmu_host.c
> @@ -371,6 +371,7 @@ static inline int kvmppc_e500_shadow_map(struct
> kvmppc_vcpu_e500 *vcpu_e500,
>
> unsigned long start, end;
> unsigned long slot_start, slot_end;
> + int tsize_inc;
>
> pfnmap = 1;
>
> @@ -392,10 +393,20 @@ static inline int kvmppc_e500_shadow_map(struct
> kvmppc_vcpu_e500 *vcpu_e500,
> MAS1_TSIZE_SHIFT;
>
> /*
> - * e500 doesn't implement the lowest tsize bit,
> - * or 1K pages.
> + * MMUv1 doesn't implement the lowest tsize bit,
> + * or translations smaller than 4K.
> */
> - tsize = max(BOOK3E_PAGESZ_4K, tsize & ~1);
> + if (!has_feature(&vcpu_e500->vcpu, VCPU_FTR_MMU_V2))
> + tsize &= ~1;
> + tsize = max(BOOK3E_PAGESZ_4K, tsize);
> +
> + /*
> + * Calculate TSIZE increment. MMUv2 supports
> + * power of 2K translations while MMUv1 is limited
> + * to power of 4K sizes.
> + */
> + tsize_inc = has_feature(&vcpu_e500->vcpu,
> + VCPU_FTR_MMU_V2) ? 1 : 2;
If you calculate tsize_inc first, then the previous if-statement can become
"tsize &= ~(tsize_inc - 1);".
>
> /*
> * Now find the largest tsize (up to what the guest
> @@ -404,7 +415,8 @@ static inline int kvmppc_e500_shadow_map(struct
> kvmppc_vcpu_e500 *vcpu_e500,
> * aligned.
> */
>
> - for (; tsize > BOOK3E_PAGESZ_4K; tsize -= 2) {
> + for (; tsize > BOOK3E_PAGESZ_4K;
> + tsize -= tsize_inc) {
> unsigned long gfn_start, gfn_end;
> tsize_pages = 1 << (tsize - 2);
>
> @@ -437,10 +449,12 @@ static inline int kvmppc_e500_shadow_map(struct
> kvmppc_vcpu_e500 *vcpu_e500,
> tsize = min(__ilog2(psize) - 10, tsize);
>
> /*
> - * e500 doesn't implement the lowest tsize bit,
> - * or 1K pages.
> + * MMUv1 doesn't implement the lowest tsize bit,
> + * or translations smaller than 4K.
> */
This comment makes it sound like MMUv2 might support translations smaller
than 4K.
-Scott
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