On Fri, Jun 02, 2023, Anish Moorthy wrote:
> When the memslot flag is enabled, fail guest memory accesses for which
> fast-gup fails (ie, where resolving the page fault would require putting
> the faulting thread to sleep).
>
> Suggested-by: James Houghton <jthoughton@xxxxxxxxxx>
> Signed-off-by: Anish Moorthy <amoorthy@xxxxxxxxxx>
> ---
> Documentation/virt/kvm/api.rst | 2 +-
> arch/x86/kvm/mmu/mmu.c | 17 ++++++++++++-----
> arch/x86/kvm/x86.c | 1 +
> 3 files changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 9daadbe2c7ed..aa7b4024fd41 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -7783,7 +7783,7 @@ bugs and reported to the maintainers so that annotations can be added.
> 7.35 KVM_CAP_NOWAIT_ON_FAULT
> ----------------------------
>
> -:Architectures: None
> +:Architectures: x86
> :Returns: -EINVAL.
>
> The presence of this capability indicates that userspace may pass the
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index cb71aae9aaec..288008a64e5c 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4299,7 +4299,9 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
> kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true, NULL);
> }
>
> -static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> +static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu,
> + struct kvm_page_fault *fault,
> + bool nowait)
More booleans!? Just say no! And in this case, there's no reason to pass in a
flag, just handle this entirely in __kvm_faultin_pfn().
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 7b6eab6f84e8..ebf21f1f43ce 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4302,6 +4302,7 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
{
struct kvm_memory_slot *slot = fault->slot;
+ bool nowait = kvm_is_slot_nowait_on_fault(slot);
bool async;
/*
@@ -4332,9 +4333,12 @@ 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, false, &async,
- fault->write, &fault->map_writable,
- &fault->hva);
+
+ fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn,
+ nowait, false,
+ nowait ? NULL : &async,
+ fault->write, &fault->map_writable, &fault->hva);
+
if (!async)
return RET_PF_CONTINUE; /* *pfn has correct page already */
On a related topic, I would *love* for someone to overhaul gfn_to_pfn() to replace
the "booleans for everything" approach and instead have KVM pass FOLL_* flags
internally. Rough sketch here: https://lkml.kernel.org/r/ZGvUsf7lMkrNDHuE%40google.com
