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Date: Thu, 13 Jan 2022 15:42:19 +0800
From: Gavin Shan <gshan@...hat.com>
To: Eric Auger <eauger@...hat.com>, kvmarm@...ts.cs.columbia.edu
Cc: kvm@...r.kernel.org, maz@...nel.org, linux-kernel@...r.kernel.org,
shan.gavin@...il.com, Jonathan.Cameron@...wei.com,
pbonzini@...hat.com, vkuznets@...hat.com, will@...nel.org
Subject: Re: [PATCH v4 03/15] KVM: async_pf: Make GFN slot management generic
Hi Eric,
On 11/11/21 1:00 AM, Eric Auger wrote:
> 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
Ok.
>>
>> * 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
Ok.
>> and removing.
> find, add, remove ops are renamed with _slot suffix
Ok. The commit log will be improved based on your suggestions in
next respin :)
>>
>> * 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@...hat.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?
Sure, lets have kvm_async_pf_reset_all_slots() in next respin.
>> +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,
Gavin
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