Re: [PATCH v2 4/7] KVM: arm64: Implement kvm_arch_flush_remote_tlbs_range()

Oliver Upton
2023-03-30T00:53:17Z

On Mon, Feb 06, 2023 at 05:23:37PM +0000, Raghavendra Rao Ananta wrote:
> Implement kvm_arch_flush_remote_tlbs_range() for arm64,
> such that it can utilize the TLBI range based instructions
> if supported.
>
> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> ---
> arch/arm64/include/asm/kvm_host.h | 3 +++
> arch/arm64/kvm/mmu.c | 15 +++++++++++++++
> 2 files changed, 18 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index dee530d75b957..211fab0c1de74 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -1002,6 +1002,9 @@ struct kvm *kvm_arch_alloc_vm(void);
> #define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS
> int kvm_arch_flush_remote_tlbs(struct kvm *kvm);
>
> +#define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS_RANGE
> +int kvm_arch_flush_remote_tlbs_range(struct kvm *kvm, gfn_t start_gfn, u64 pages);
> +
> static inline bool kvm_vm_is_protected(struct kvm *kvm)
> {
> return false;
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index e98910a8d0af6..409cb187f4911 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -91,6 +91,21 @@ int kvm_arch_flush_remote_tlbs(struct kvm *kvm)
> return 0;
> }
>
> +int kvm_arch_flush_remote_tlbs_range(struct kvm *kvm, gfn_t start_gfn, u64 pages)
> +{
> + phys_addr_t start, end;
> +
> + if (!system_supports_tlb_range())
> + return -EOPNOTSUPP;

There's multiple layers of fallback throughout this series, as it would
appear that deep in __kvm_tlb_flush_range() you're blasting the whole
VMID if either the range is too large or the feature isn't supported.

Is it possible to just normalize on a single spot to gate the use of
range-based invalidations? I have a slight preference for doing it deep
in the handler, as it keeps the upper layers of code a bit more
readable.

> + start = start_gfn << PAGE_SHIFT;
> + end = (start_gfn + pages) << PAGE_SHIFT;
> +
> + kvm_call_hyp(__kvm_tlb_flush_range_vmid_ipa, &kvm->arch.mmu,
> + start, end, KVM_PGTABLE_MAX_LEVELS - 1, 0);
> + return 0;
> +}
> +
> static bool kvm_is_device_pfn(unsigned long pfn)
> {
> return !pfn_is_map_memory(pfn);
> --
> 2.39.1.519.gcb327c4b5f-goog
>
>

--
Thanks,
Oliver