Re: [PATCH v4 03/15] KVM: async_pf: Make GFN slot management generic

From: Eric Auger
Date: Wed Nov 10 2021 - 12:00:35 EST

Hi Gavin,

On 8/15/21 2:59 AM, Gavin Shan wrote:
> It's not allowed to fire duplicate notification for same GFN on
> x86 platform, with help of a hash table. This mechanism is going
s/, with help of a hash table/this is achieved through a hash table
> to be used by arm64 and this makes the code generic and shareable
s/and this makes/.\n Turn the code generic
> by multiple platforms.
>
> * As this mechanism isn't needed by all platforms, a new kernel
> config option (CONFIG_ASYNC_PF_SLOT) is introduced so that it
> can be disabled at compiling time.
compile time
>
> * The code is basically copied from x86 platform and the functions
> are renamed to reflect the fact: (a) the input parameters are
> vCPU and GFN.
not for reset
(b) The operations are resetting, searching, adding
> and removing.
find, add, remove ops are renamed with _slot suffix
>
> * Helper stub is also added on !CONFIG_KVM_ASYNC_PF because we're
> going to use IS_ENABLED() instead of #ifdef on arm64 when the
> asynchronous page fault is supported.
>
> This is preparatory work to use the newly introduced functions on x86
> platform and arm64 in subsequent patches.
>
> Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
> ---
> include/linux/kvm_host.h | 18 +++++++++
> virt/kvm/Kconfig | 3 ++
> virt/kvm/async_pf.c | 85 ++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 106 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index a5f990f6dc35..a9685c2b2250 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -298,6 +298,9 @@ struct kvm_vcpu {
>
> #ifdef CONFIG_KVM_ASYNC_PF
> struct {
> +#ifdef CONFIG_KVM_ASYNC_PF_SLOT
> + gfn_t gfns[ASYNC_PF_PER_VCPU];
> +#endif
> u32 queued;
> struct list_head queue;
> struct list_head done;
> @@ -339,6 +342,13 @@ struct kvm_async_pf {
> bool notpresent_injected;
> };
>
> +#ifdef CONFIG_KVM_ASYNC_PF_SLOT
> +void kvm_async_pf_reset_slot(struct kvm_vcpu *vcpu);
this does not reset a "slot" but the whole hash table. So to me this
shouldn't be renamed with _slot suffix. reset_hash or reset_all_slots?
> +void kvm_async_pf_add_slot(struct kvm_vcpu *vcpu, gfn_t gfn);
> +void kvm_async_pf_remove_slot(struct kvm_vcpu *vcpu, gfn_t gfn);
> +bool kvm_async_pf_find_slot(struct kvm_vcpu *vcpu, gfn_t gfn);
> +#endif
> +
> static inline bool kvm_check_async_pf_completion_queue(struct kvm_vcpu *vcpu)
> {
> return !list_empty_careful(&vcpu->async_pf.done);
> @@ -350,6 +360,14 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> unsigned long hva, struct kvm_arch_async_pf *arch);
> int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> #else
> +static inline void kvm_async_pf_reset_slot(struct kvm_vcpu *vcpu) { }
> +static inline void kvm_async_pf_add_slot(struct kvm_vcpu *vcpu, gfn_t gfn) { }
> +static inline void kvm_async_pf_remove_slot(struct kvm_vcpu *vcpu, gfn_t gfn) { }
> +static inline bool kvm_async_pf_find_slot(struct kvm_vcpu *vcpu, gfn_t gfn)
> +{
> + return false;
> +}
> +
> static inline bool kvm_check_async_pf_completion_queue(struct kvm_vcpu *vcpu)
> {
> return false;
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index 62b39149b8c8..59b518c8c205 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -23,6 +23,9 @@ config KVM_MMIO
> config KVM_ASYNC_PF
> bool
>
> +config KVM_ASYNC_PF_SLOT
> + bool
> +
> # Toggle to switch between direct notification and batch job
> config KVM_ASYNC_PF_SYNC
> bool
> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
> index d145a61a046a..0d1fdb2932af 100644
> --- a/virt/kvm/async_pf.c
> +++ b/virt/kvm/async_pf.c
> @@ -13,12 +13,97 @@
> #include <linux/module.h>
> #include <linux/mmu_context.h>
> #include <linux/sched/mm.h>
> +#ifdef CONFIG_KVM_ASYNC_PF_SLOT
> +#include <linux/hash.h>
> +#endif
>
> #include "async_pf.h"
> #include <trace/events/kvm.h>
>
> static struct kmem_cache *async_pf_cache;
>
> +#ifdef CONFIG_KVM_ASYNC_PF_SLOT
> +static inline u32 kvm_async_pf_hash(gfn_t gfn)
> +{
> + BUILD_BUG_ON(!is_power_of_2(ASYNC_PF_PER_VCPU));
> +
> + return hash_32(gfn & 0xffffffff, order_base_2(ASYNC_PF_PER_VCPU));
> +}
> +
> +static inline u32 kvm_async_pf_next_slot(u32 key)
> +{
> + return (key + 1) & (ASYNC_PF_PER_VCPU - 1);
> +}
> +
> +static u32 kvm_async_pf_slot(struct kvm_vcpu *vcpu, gfn_t gfn)
> +{
> + u32 key = kvm_async_pf_hash(gfn);
> + int i;
> +
> + for (i = 0; i < ASYNC_PF_PER_VCPU &&
> + (vcpu->async_pf.gfns[key] != gfn &&
> + vcpu->async_pf.gfns[key] != ~0); i++)
> + key = kvm_async_pf_next_slot(key);
> +
> + return key;
> +}
> +
> +void kvm_async_pf_reset_slot(struct kvm_vcpu *vcpu)
> +{
> + int i;
> +
> + for (i = 0; i < ASYNC_PF_PER_VCPU; i++)
> + vcpu->async_pf.gfns[i] = ~0;
> +}
> +
> +void kvm_async_pf_add_slot(struct kvm_vcpu *vcpu, gfn_t gfn)
> +{
> + u32 key = kvm_async_pf_hash(gfn);
> +
> + while (vcpu->async_pf.gfns[key] != ~0)
> + key = kvm_async_pf_next_slot(key);
> +
> + vcpu->async_pf.gfns[key] = gfn;
> +}
> +
> +void kvm_async_pf_remove_slot(struct kvm_vcpu *vcpu, gfn_t gfn)
> +{
> + u32 i, j, k;
> +
> + i = j = kvm_async_pf_slot(vcpu, gfn);
> +
> + if (WARN_ON_ONCE(vcpu->async_pf.gfns[i] != gfn))
> + return;
> +
> + while (true) {
> + vcpu->async_pf.gfns[i] = ~0;
> +
> + do {
> + j = kvm_async_pf_next_slot(j);
> + if (vcpu->async_pf.gfns[j] == ~0)
> + return;
> +
> + k = kvm_async_pf_hash(vcpu->async_pf.gfns[j]);
> + /*
> + * k lies cyclically in ]i,j]
> + * | i.k.j |
> + * |....j i.k.| or |.k..j i...|
> + */
> + } while ((i <= j) ? (i < k && k <= j) : (i < k || k <= j));
> +
> + vcpu->async_pf.gfns[i] = vcpu->async_pf.gfns[j];
> + i = j;
> + }
> +}
> +
> +bool kvm_async_pf_find_slot(struct kvm_vcpu *vcpu, gfn_t gfn)
> +{
> + u32 key = kvm_async_pf_slot(vcpu, gfn);
> +
> + return vcpu->async_pf.gfns[key] == gfn;
> +}
> +#endif /* CONFIG_KVM_ASYNC_PF_SLOT */
> +
> int kvm_async_pf_init(void)
> {
> async_pf_cache = KMEM_CACHE(kvm_async_pf, 0);
>
Thanks

Eric