On Wed, Jun 22, 2022, Peter Xu wrote:
> Add one new PFN error type to show when we cannot finish fetching the PFN
> due to interruptions. For example, by receiving a generic signal.
>
> This prepares KVM to be able to respond to SIGUSR1 (for QEMU that's the
> SIGIPI) even during e.g. handling an userfaultfd page fault.
>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
> include/linux/kvm_host.h | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index b646b6fcaec6..4f84a442f67f 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -96,6 +96,7 @@
> #define KVM_PFN_ERR_FAULT (KVM_PFN_ERR_MASK)
> #define KVM_PFN_ERR_HWPOISON (KVM_PFN_ERR_MASK + 1)
> #define KVM_PFN_ERR_RO_FAULT (KVM_PFN_ERR_MASK + 2)
> +#define KVM_PFN_ERR_INTR (KVM_PFN_ERR_MASK + 3)
>
> /*
> * error pfns indicate that the gfn is in slot but faild to
> @@ -106,6 +107,16 @@ static inline bool is_error_pfn(kvm_pfn_t pfn)
> return !!(pfn & KVM_PFN_ERR_MASK);
> }
>
> +/*
> + * When KVM_PFN_ERR_INTR is returned, it means we're interrupted during
> + * fetching the PFN (e.g. a signal might have arrived), so we may want to
> + * retry at some later point and kick the userspace to handle the signal.
> + */
> +static inline bool is_intr_pfn(kvm_pfn_t pfn)
> +{
> + return pfn == KVM_PFN_ERR_INTR;
What about is_sigpending_pfn() and KVM_PFN_ERR_SIGPENDING? "intr" is too close to
a real thing KVM will encounter, and I think knowing that KVM is effectively
responding to a pending signal is the most important detail for KVM developers
encountering this code for this first time. E.g. from KVM_PFN_ERR_INTR alone, one
might think that any interrupt during GUP will trigger this.
> +}
> +
> /*
> * error_noslot pfns indicate that the gfn can not be
> * translated to pfn - it is not in slot or failed to
> --
> 2.32.0
>
