Re: [PATCH 4/5] KVM: Add hypercall queue for paravirt_ops implementation

Anthony Liguori
2007-06-18T12:22:12Z

Jeremy Fitzhardinge wrote:
> Anthony Liguori wrote:
>
>> Regards,
>>
>> Anthony Liguori
>> ------------------------------------------------------------------------
>>
>> Subject: [PATCH] KVM: Add hypercall queue for paravirt_ops implementation
>> Author: Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
>>
>> Implemented a hypercall queue that can be used when paravirt_ops lazy mode
>> is enabled. This patch enables queueing of MMU write operations and CR
>> updates. This results in about a 50% bump in kernbench performance.
>>
>> Signed-off-by: Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
>>
>> diff --git a/arch/i386/kernel/kvm.c b/arch/i386/kernel/kvm.c
>> index 07ce38e..4b323f1 100644
>> --- a/arch/i386/kernel/kvm.c
>> +++ b/arch/i386/kernel/kvm.c
>> @@ -33,8 +33,10 @@ struct kvm_paravirt_state
>> unsigned long cached_cr[5];
>> int cr_valid[5];
>>
>> - struct kvm_vmca *vmca;
>> + enum paravirt_lazy_mode mode;
>> struct kvm_hypercall_entry *queue;
>> +
>> + struct kvm_vmca *vmca;
>> void (*hypercall)(void);
>>
>> u64 vmca_gpa;
>> @@ -42,17 +44,17 @@ struct kvm_paravirt_state
>>
>> static DEFINE_PER_CPU(struct kvm_paravirt_state *, paravirt_state);
>>
>> +static int do_hypercall_batching;
>> static int do_mmu_write;
>> static int do_cr_read_caching;
>> static int do_nop_io_delay;
>> static u64 msr_set_vmca;
>>
>> -static long kvm_hypercall(unsigned int nr, unsigned long p1,
>> - unsigned long p2, unsigned long p3,
>> - unsigned long p4)
>> +static long _kvm_hypercall(struct kvm_paravirt_state *state,
>> + unsigned int nr, unsigned long p1,
>> + unsigned long p2, unsigned long p3,
>> + unsigned long p4)
>> {
>> - struct kvm_paravirt_state *state
>> - = per_cpu(paravirt_state, smp_processor_id());
>> long ret;
>>
>> asm volatile("call *(%6) \n\t"
>> @@ -69,6 +71,55 @@ static long kvm_hypercall(unsigned int nr, unsigned long p1,
>> return ret;
>> }
>>
>> +static int can_defer_hypercall(struct kvm_paravirt_state *state,
>> + unsigned int nr)
>> +{
>> + if (state->mode == PARAVIRT_LAZY_MMU) {
>> + if (nr == KVM_HYPERCALL_MMU_WRITE)
>> + return 1;
>> + } else if (state->mode == PARAVIRT_LAZY_CPU) {
>> + if (nr == KVM_HYPERCALL_SET_CR)
>> + return 1;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static void _kvm_hypercall_defer(struct kvm_paravirt_state *state,
>> + unsigned int nr,
>> + unsigned long p1, unsigned long p2,
>> + unsigned long p3, unsigned long p4)
>> +{
>> + struct kvm_hypercall_entry *entry;
>> +
>> + if (state->vmca->queue_index == state->vmca->max_queue_index)
>> + _kvm_hypercall(state, KVM_HYPERCALL_FLUSH, 0, 0, 0, 0);
>> +
>> + /* FIXME: are we preempt safe here? */
>>
>>
>
> BUG_ON(preemptible()) would be a reasonable thing to put here to be sure.
>

Ok.

>> + entry = &state->queue[state->vmca->queue_index++];
>> + entry->nr = nr;
>> + entry->p1 = p1;
>> + entry->p2 = p2;
>> + entry->p3 = p3;
>> + entry->p4 = p4;
>> +}
>> +
>> +static long kvm_hypercall(unsigned int nr, unsigned long p1,
>> + unsigned long p2, unsigned long p3,
>> + unsigned long p4)
>> +{
>> + struct kvm_paravirt_state *state
>> + = per_cpu(paravirt_state, smp_processor_id());
>>
>>
>
> Rather than using this here and passing state around, you could use
> either x86_read/write_percpu, or get/put_cpu_var (or __get_vpu_var if
> you don't need the preempt-disable).
>

Ok.

>> + long ret = 0;
>> +
>> + if (can_defer_hypercall(state, nr))
>> + _kvm_hypercall_defer(state, nr, p1, p2, p3, p4);
>> + else
>> + ret = _kvm_hypercall(state, nr, p1, p2, p3, p4);
>> +
>> + return ret;
>> +}
>> +
>> /*
>> * No need for any "IO delay" on KVM
>> */
>> @@ -107,7 +158,9 @@ static void kvm_write_cr(int reg, unsigned long value)
>> state->cr_valid[reg] = 1;
>> state->cached_cr[reg] = value;
>>
>> - if (reg == 0)
>> + if (state->mode == PARAVIRT_LAZY_CPU)
>> + kvm_hypercall(KVM_HYPERCALL_SET_CR, reg, value, 0, 0);
>> + else if (reg == 0)
>> native_write_cr0(value);
>> else if (reg == 3)
>> native_write_cr3(value);
>> @@ -218,6 +271,18 @@ static void kvm_pmd_clear(pmd_t *pmdp)
>> kvm_mmu_write(pmdp, &pmd, sizeof(pmd));
>> }
>>
>> +static void kvm_set_lazy_mode(enum paravirt_lazy_mode mode)
>> +{
>> + struct kvm_paravirt_state *state
>> + = per_cpu(paravirt_state, smp_processor_id());
>> +
>> + if (mode == PARAVIRT_LAZY_FLUSH || mode == PARAVIRT_LAZY_NONE) {
>> + if (state->vmca->queue_index)
>> + _kvm_hypercall(state, KVM_HYPERCALL_FLUSH, 0, 0, 0, 0);
>> + }
>> + state->mode = mode;
>>
>>
>
> No, you don't want to set state->mode to LAZY_FLUSH (its not a mode,
> just a action which overloads the interface).
>

Thanks, I wasn't aware of that.

>> +}
>> +
>> static void paravirt_ops_setup(void)
>> {
>> paravirt_ops.name = "KVM";
>> @@ -249,6 +314,9 @@ static void paravirt_ops_setup(void)
>> paravirt_ops.set_pud = kvm_set_pud;
>> }
>>
>> + if (do_hypercall_batching)
>> + paravirt_ops.set_lazy_mode = kvm_set_lazy_mode;
>> +
>> paravirt_ops.paravirt_enabled = 1;
>>
>> apply_paravirt(__parainstructions, __parainstructions_end);
>> @@ -293,6 +361,9 @@ static int paravirt_initialize(void)
>> if ((edx & KVM_FEATURE_MMU_WRITE))
>> do_mmu_write = 1;
>>
>> + if ((edx & KVM_FEATURE_HYPERCALL_BATCHING))
>> + do_hypercall_batching = 1;
>> +
>> on_each_cpu(paravirt_activate, NULL, 0, 1);
>>
>> return 0;
>> @@ -303,6 +374,9 @@ static __init void paravirt_free_state(struct kvm_paravirt_state *state)
>> if (!state)
>> return;
>>
>> + if (state->queue)
>> + __free_page(pfn_to_page(__pa(state->queue) >> PAGE_SHIFT));
>> +
>> if (state->hypercall)
>> __free_page(pfn_to_page(__pa(state->hypercall) >> PAGE_SHIFT));
>>
>> @@ -329,8 +403,15 @@ static __init struct kvm_paravirt_state *paravirt_alloc_state(void)
>> if (!state->hypercall)
>> goto err;
>>
>> + state->queue = (void *)get_zeroed_page(GFP_KERNEL);
>> + if (!state->queue)
>> + goto err;
>> +
>> state->vmca_gpa = __pa(state->vmca);
>> state->vmca->hypercall_gpa = __pa(state->hypercall);
>> + state->vmca->queue_gpa = __pa(state->queue);
>> + state->vmca->max_queue_index
>> + = (PAGE_SIZE / sizeof(struct kvm_hypercall_entry));
>>
>> return state;
>>
>> diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
>> index b08272b..d531899 100644
>> --- a/drivers/kvm/kvm.h
>> +++ b/drivers/kvm/kvm.h
>> @@ -291,6 +291,7 @@ struct kvm_vcpu {
>> gpa_t para_state_gpa;
>> struct page *para_state_page;
>> gpa_t hypercall_gpa;
>> + struct page *queue_page;
>> unsigned long cr4;
>> unsigned long cr8;
>> u64 pdptrs[4]; /* pae */
>> diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
>> index 4f65729..79a2a64 100644
>> --- a/drivers/kvm/kvm_main.c
>> +++ b/drivers/kvm/kvm_main.c
>> @@ -94,7 +94,8 @@ struct vfsmount *kvmfs_mnt;
>>
>> #define KVM_PARAVIRT_FEATURES \
>> (KVM_FEATURE_VMCA | KVM_FEATURE_NOP_IO_DELAY | \
>> - KVM_FEATURE_CR_READ_CACHE | KVM_FEATURE_MMU_WRITE)
>> + KVM_FEATURE_CR_READ_CACHE | KVM_FEATURE_MMU_WRITE | \
>> + KVM_FEATURE_HYPERCALL_BATCHING)
>>
>> #define KVM_MSR_SET_VMCA 0x87655678
>>
>> @@ -1369,6 +1370,24 @@ static int kvm_hypercall_mmu_write(struct kvm_vcpu *vcpu, gva_t addr,
>> return 0;
>> }
>>
>> +static int kvm_hypercall_set_cr(struct kvm_vcpu *vcpu,
>> + u32 reg, unsigned long value)
>> +{
>> + switch (reg) {
>> + case 0:
>> + set_cr0(vcpu, value);
>> + break;
>> + case 3:
>> + set_cr3(vcpu, value);
>> + break;
>> + case 4:
>> + set_cr4(vcpu, value);
>> + break;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> static int dispatch_hypercall(struct kvm_vcpu *vcpu, unsigned long nr,
>> unsigned long p1, unsigned long p2,
>> unsigned long p3, unsigned long p4)
>> @@ -1376,10 +1395,36 @@ static int dispatch_hypercall(struct kvm_vcpu *vcpu, unsigned long nr,
>> switch (nr) {
>> case KVM_HYPERCALL_MMU_WRITE:
>> return kvm_hypercall_mmu_write(vcpu, p1, p2, p3, p4);
>> + case KVM_HYPERCALL_SET_CR:
>> + return kvm_hypercall_set_cr(vcpu, p1, p2);
>> }
>> return -ENOSYS;
>> }
>>
>> +static int kvm_hypercall_flush(struct kvm_vcpu *vcpu)
>> +{
>> + struct kvm_hypercall_entry *queue;
>> + struct kvm_vmca *vmca;
>> + int ret = 0;
>> + int i;
>> +
>> + queue = kmap(vcpu->queue_page);
>> + vmca = kmap(vcpu->para_state_page);
>>
>>
>
> kmap_atomic? Or why not keep them mapped all the time?
>

On the kvm side, this ends up calling emulator_write_phys() which IIRC
can potentially sleep.

Regards,

Anthony Liguori

> J