Re: [PATCH v2 2/7] KVM: arm64: Add FEAT_TLBIRANGE support

Oliver Upton
2023-03-30T01:19:20Z

On Mon, Feb 06, 2023 at 05:23:35PM +0000, Raghavendra Rao Ananta wrote:
> Define a generic function __kvm_tlb_flush_range() to
> invalidate the TLBs over a range of addresses. The
> implementation accepts 'op' as a generic TLBI operation.
> Upcoming patches will use this to implement IPA based
> TLB invalidations (ipas2e1is).
>
> If the system doesn't support FEAT_TLBIRANGE, the
> implementation falls back to flushing the pages one by one
> for the range supplied.
>
> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> ---
> arch/arm64/include/asm/kvm_asm.h | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 43c3bc0f9544d..995ff048e8851 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -221,6 +221,24 @@ DECLARE_KVM_NVHE_SYM(__per_cpu_end);
> DECLARE_KVM_HYP_SYM(__bp_harden_hyp_vecs);
> #define __bp_harden_hyp_vecs CHOOSE_HYP_SYM(__bp_harden_hyp_vecs)
>
> +#define __kvm_tlb_flush_range(op, mmu, start, end, level, tlb_level) do { \
> + unsigned long pages, stride; \
> + \
> + stride = kvm_granule_size(level); \

Hmm... There's a rather subtle and annoying complication here that I
don't believe is handled.

Similar to what I said in the last spin of the series, there is no
guarantee that a range of IPAs is mapped at the exact same level
throughout. Dirty logging and memslots that aren't hugepage aligned
could lead to a mix of mapping levels being used within a range of the
IPA space.

> + start = round_down(start, stride); \
> + end = round_up(end, stride); \
> + pages = (end - start) >> PAGE_SHIFT; \
> + \
> + if ((!system_supports_tlb_range() && \
> + (end - start) >= (MAX_TLBI_OPS * stride)) || \

Doesn't checking for TLBIRANGE above eliminate the need to test against
MAX_TLBI_OPS?

> + pages >= MAX_TLBI_RANGE_PAGES) { \
> + __kvm_tlb_flush_vmid(mmu); \
> + break; \
> + } \
> + \
> + __flush_tlb_range_op(op, start, pages, stride, 0, tlb_level, false); \
> +} while (0)
> +
> extern void __kvm_flush_vm_context(void);
> extern void __kvm_flush_cpu_context(struct kvm_s2_mmu *mmu);
> extern void __kvm_tlb_flush_vmid_ipa(struct kvm_s2_mmu *mmu, phys_addr_t ipa,
> --
> 2.39.1.519.gcb327c4b5f-goog
>
>

--
Thanks,
Oliver