On 16/04/20 17:58, Peter Xu wrote:
> Forcing the ASYNC_PF_PER_VCPU to be power of two is much easier to be
> used rather than calling roundup_pow_of_two() from time to time. Do
> this by adding a BUILD_BUG_ON() inside the hash function.
>
> Another point is that generally async pf does not allow concurrency
> over ASYNC_PF_PER_VCPU after all (see kvm_setup_async_pf()), so it
> does not make much sense either to have it not a power of two or some
> of the entries will definitely be wasted.
>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
> arch/x86/include/asm/kvm_host.h | 2 +-
> arch/x86/kvm/x86.c | 8 +++++---
> 2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 42a2d0d3984a..9f0fdaacdfa5 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -761,7 +761,7 @@ struct kvm_vcpu_arch {
>
> struct {
> bool halted;
> - gfn_t gfns[roundup_pow_of_two(ASYNC_PF_PER_VCPU)];
> + gfn_t gfns[ASYNC_PF_PER_VCPU];
> struct gfn_to_hva_cache data;
> u64 msr_val;
> u32 id;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b8124b562dea..fc74dafa72ff 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -261,7 +261,7 @@ static int emulator_fix_hypercall(struct x86_emulate_ctxt *ctxt);
> static inline void kvm_async_pf_hash_reset(struct kvm_vcpu *vcpu)
> {
> int i;
> - for (i = 0; i < roundup_pow_of_two(ASYNC_PF_PER_VCPU); i++)
> + for (i = 0; i < ASYNC_PF_PER_VCPU; i++)
> vcpu->arch.apf.gfns[i] = ~0;
> }
>
> @@ -10265,12 +10265,14 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
>
> static inline u32 kvm_async_pf_hash_fn(gfn_t gfn)
> {
> + BUILD_BUG_ON(!is_power_of_2(ASYNC_PF_PER_VCPU));
> +
> return hash_32(gfn & 0xffffffff, order_base_2(ASYNC_PF_PER_VCPU));
> }
>
> static inline u32 kvm_async_pf_next_probe(u32 key)
> {
> - return (key + 1) & (roundup_pow_of_two(ASYNC_PF_PER_VCPU) - 1);
> + return (key + 1) & (ASYNC_PF_PER_VCPU - 1);
> }
>
> static void kvm_add_async_pf_gfn(struct kvm_vcpu *vcpu, gfn_t gfn)
> @@ -10288,7 +10290,7 @@ static u32 kvm_async_pf_gfn_slot(struct kvm_vcpu *vcpu, gfn_t gfn)
> int i;
> u32 key = kvm_async_pf_hash_fn(gfn);
>
> - for (i = 0; i < roundup_pow_of_two(ASYNC_PF_PER_VCPU) &&
> + for (i = 0; i < ASYNC_PF_PER_VCPU &&
> (vcpu->arch.apf.gfns[key] != gfn &&
> vcpu->arch.apf.gfns[key] != ~0); i++)
> key = kvm_async_pf_next_probe(key);
>
Queued, thanks.
Paolo
