Re: [PATCH v2 05/19] KVM: arm64: Add helpers to manipulate vcpu flags among a set

Reiji Watanabe
2022-06-11T18:38:12Z

On Fri, Jun 10, 2022 at 2:28 AM Marc Zyngier <maz@kernel.org> wrote:
>
> Careful analysis of the vcpu flags show that this is a mix of
> configuration, communication between the host and the hypervisor,
> as well as anciliary state that has no consistency. It'd be a lot
> better if we could split these flags into consistent categories.
>
> However, even if we split these flags apart, we want to make sure
> that each flag can only be applied to its own set, and not across
> sets.
>
> To achieve this, use a preprocessor hack so that each flag is always
> associated with:
>
> - the set that contains it,
>
> - a mask that describe all the bits that contain it (for a simple
> flag, this is the same thing as the flag itself, but we will
> eventually have values that cover multiple bits at once).
>
> Each flag is thus a triplet that is not directly usable as a value,
> but used by three helpers that allow the flag to be set, cleared,
> and fetched. By mandating the use of such helper, we can easily
> enforce that a flag can only be used with the set it belongs to.
>
> Finally, one last helper "unpacks" the raw value from the triplet
> that represents a flag, which is useful for multi-bit values that
> need to be enumerated (in a switch statement, for example).
>
> Further patches will start making use of this infrastructure.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/include/asm/kvm_host.h | 44 +++++++++++++++++++++++++++++++
> 1 file changed, 44 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 372c5642cfab..6d30ac7e3164 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -415,6 +415,50 @@ struct kvm_vcpu_arch {
> } steal;
> };
>
> +/*
> + * Each 'flag' is composed of a comma-separated triplet:
> + *
> + * - the flag-set it belongs to in the vcpu->arch structure
> + * - the value for that flag
> + * - the mask for that flag
> + *
> + * __vcpu_single_flag() builds such a triplet for a single-bit flag.
> + * unpack_vcpu_flag() extract the flag value from the triplet for
> + * direct use outside of the flag accessors.
> + */
> +#define __vcpu_single_flag(_set, _f) _set, (_f), (_f)
> +
> +#define __unpack_flag(_set, _f, _m) _f
> +#define unpack_vcpu_flag(...) __unpack_flag(__VA_ARGS__)
> +
> +#define __vcpu_get_flag(v, flagset, f, m) \
> + ({ \
> + v->arch.flagset & (m); \
> + })
> +
> +#define __vcpu_set_flag(v, flagset, f, m) \
> + do { \
> + typeof(v->arch.flagset) *fset; \
> + \
> + fset = &v->arch.flagset; \
> + if (HWEIGHT(m) > 1) \
> + *fset &= ~(m); \
> + *fset |= (f); \
> + } while (0)
> +
> +#define __vcpu_clear_flag(v, flagset, f, m) \
> + do { \
> + typeof(v->arch.flagset) *fset; \
> + \
> + fset = &v->arch.flagset; \
> + *fset &= ~(m); \
> + } while (0)

Reviewed-by: Reiji Watanabe <reijiw@google.com>

IMHO I would prefer to have 'v' enclosed in parentheses in the
implementation of __vcpu_{get,set,clear}_flag rather than in
the implementation of vcpu_{get,set,clear}_flag though.
(That was what I meant in my comment for v1)

Thanks,
Reiji

> +#define vcpu_get_flag(v, ...) __vcpu_get_flag((v), __VA_ARGS__)
> +#define vcpu_set_flag(v, ...) __vcpu_set_flag((v), __VA_ARGS__)
> +#define vcpu_clear_flag(v, ...) __vcpu_clear_flag((v), __VA_ARGS__)
> +
> +
> /* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */
> #define vcpu_sve_pffr(vcpu) (kern_hyp_va((vcpu)->arch.sve_state) + \
> sve_ffr_offset((vcpu)->arch.sve_max_vl))
> --
> 2.34.1
>