Subject: Re: [PATCH v4 03/15] KVM: async_pf: Make GFN slot management generic
To:     Gavin Shan <gshan@redhat.com>, kvmarm@lists.cs.columbia.edu
Cc:     kvm@vger.kernel.org, maz@kernel.org, linux-kernel@vger.kernel.org,
        shan.gavin@gmail.com, Jonathan.Cameron@huawei.com,
        pbonzini@redhat.com, vkuznets@redhat.com, will@kernel.org
References: <20210815005947.83699-1-gshan@redhat.com>
 <20210815005947.83699-4-gshan@redhat.com>
From:   Eric Auger <eauger@redhat.com>
Message-ID: <06cb06c0-13e7-906b-9b88-543a58bb5590@redhat.com>
Date:   Wed, 10 Nov 2021 18:00:12 +0100
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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@redhat.com>
> ---
>  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