Re: [PATCH 2/4] kvm: Merge "atomic" and "write" in __gfn_to_pfn_memslot()

From: Sean Christopherson
Date: Thu Jun 23 2022 - 10:49:58 EST


On Wed, Jun 22, 2022, Peter Xu wrote:
> Merge two boolean parameters into a bitmask flag called kvm_gtp_flag_t for
> __gfn_to_pfn_memslot(). This cleans the parameter lists, and also prepare
> for new boolean to be added to __gfn_to_pfn_memslot().

...

> @@ -3999,8 +4000,8 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> }
>
> async = false;
> - fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, &async,
> - fault->write, &fault->map_writable,
> + fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, flags,
> + &async, &fault->map_writable,
> &fault->hva);
> if (!async)
> return RET_PF_CONTINUE; /* *pfn has correct page already */
> @@ -4016,9 +4017,8 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> }
> }
>
> - fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, NULL,
> - fault->write, &fault->map_writable,
> - &fault->hva);
> + fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, flags, NULL,
> + &fault->map_writable, &fault->hva);
> return RET_PF_CONTINUE;
> }
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index c20f2d55840c..b646b6fcaec6 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1146,8 +1146,15 @@ kvm_pfn_t gfn_to_pfn_prot(struct kvm *kvm, gfn_t gfn, bool write_fault,
> bool *writable);
> kvm_pfn_t gfn_to_pfn_memslot(const struct kvm_memory_slot *slot, gfn_t gfn);
> kvm_pfn_t gfn_to_pfn_memslot_atomic(const struct kvm_memory_slot *slot, gfn_t gfn);
> +
> +/* gfn_to_pfn (gtp) flags */
> +typedef unsigned int __bitwise kvm_gtp_flag_t;
> +
> +#define KVM_GTP_WRITE ((__force kvm_gtp_flag_t) BIT(0))
> +#define KVM_GTP_ATOMIC ((__force kvm_gtp_flag_t) BIT(1))
> +
> kvm_pfn_t __gfn_to_pfn_memslot(const struct kvm_memory_slot *slot, gfn_t gfn,
> - bool atomic, bool *async, bool write_fault,
> + kvm_gtp_flag_t gtp_flags, bool *async,
> bool *writable, hva_t *hva);

I completely agree the list of booleans is a mess, but I don't love the result of
adding @flags. I wonder if we can do something similar to x86's struct kvm_page_fault
and add an internal struct to pass params. And then add e.g. gfn_to_pfn_interruptible()
to wrap that logic.

I suspect we could also clean up the @async behavior at the same time, as its
interaction with FOLL_NOWAIT is confusing.