Messages in this thread | | | Subject | Re: [PART1 RFC v2 05/10] KVM: x86: Detect and Initialize AVIC support | From | Suravee Suthikulpanit <> | Date | Wed, 16 Mar 2016 00:09:32 +0700 |
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Hi
On 03/07/2016 11:41 PM, Paolo Bonzini wrote: > On 04/03/2016 21:46, Suravee Suthikulpanit wrote: > > [....] >> +/* Note: This structure is per VM */ >> +struct svm_vm_data { >> + atomic_t count; >> + u32 ldr_mode; >> + u32 avic_max_vcpu_id; >> + u32 avic_tag; >> + >> + struct page *avic_log_ait_page; >> + struct page *avic_phy_ait_page; > > You can put these directly in kvm_arch. Do not use abbreviations: > > struct page *avic_logical_apic_id_table_page; > struct page *avic_physical_apic_id_table_page; >
Actually, the reason I would like to introduce this per-arch specific structure is because I feel that it is easier to manage these processor-specific variable/data-structure. If we add all these directly into kvm_arch, which is shared b/w SVM and VMX, it is more difficult to tell which one is used in the different code base.
>> [...] >> + memcpy(vapic_bkpg, svm->in_kernel_lapic_regs, PAGE_SIZE); >> + svm->vcpu.arch.apic->regs = vapic_bkpg; > > Can you explain the flipping logic, and why you cannot just use the > existing apic.regs?
Please see "explanation 1" below.
>> [...] >> +static struct svm_avic_phy_ait_entry * >> +avic_get_phy_ait_entry(struct kvm_vcpu *vcpu, int index) >> +{ >> + [.....] >> +} >> + >> +struct svm_avic_log_ait_entry * >> +avic_get_log_ait_entry(struct kvm_vcpu *vcpu, u8 mda, bool is_flat) >> +{ >> + [.....] >> +} > > Instead of these functions, create a complete function to handle APIC_ID > and APIC_LDR writes. Then use kmap/kunmap instead of page_address. >
Ok. May I ask why we are against using page_address? I have see that used in several places in the code.
>> [...] >> +static int avic_alloc_bk_page(struct vcpu_svm *svm, int id) >> +{ >> + int ret = 0, i; >> + bool realloc = false; >> + struct kvm_vcpu *vcpu; >> + struct kvm *kvm = svm->vcpu.kvm; >> + struct svm_vm_data *vm_data = kvm->arch.arch_data; >> + >> + mutex_lock(&kvm->slots_lock); >> + >> + /* Check if we have already allocated vAPIC backing >> + * page for this vCPU. If not, we need to realloc >> + * a new one and re-assign all other vCPU. >> + */ >> + if (kvm->arch.apic_access_page_done && >> + (id > vm_data->avic_max_vcpu_id)) { >> + kvm_for_each_vcpu(i, vcpu, kvm) >> + avic_unalloc_bk_page(vcpu); >> + >> + __x86_set_memory_region(kvm, APIC_ACCESS_PAGE_PRIVATE_MEMSLOT, >> + 0, 0); >> + realloc = true; >> + vm_data->avic_max_vcpu_id = 0; >> + } >> + >> + /* >> + * We are allocating vAPIC backing page >> + * upto the max vCPU ID >> + */ >> + if (id >= vm_data->avic_max_vcpu_id) { >> + ret = __x86_set_memory_region(kvm, >> + APIC_ACCESS_PAGE_PRIVATE_MEMSLOT, >> + APIC_DEFAULT_PHYS_BASE, >> + PAGE_SIZE * (id + 1)); > > Why is this necessary? The APIC access page is a peculiarity of Intel > processors (and the special memslot for only needs to map 0xfee00000 to > 0xfee00fff; after that there is the MSI area). >
Please see "explanation 1" below.
>> [...] >> + if (ret) >> + goto out; >> + >> + vm_data->avic_max_vcpu_id = id; >> + } >> + >> + /* Reinit vAPIC backing page for exisinting vcpus */ >> + if (realloc) >> + kvm_for_each_vcpu(i, vcpu, kvm) >> + avic_init_bk_page(vcpu); > > Why is this necessary?
Explanation 1:
The current lapic regs page is allocated using get_zeroed_page(), which can be paged out. If I use these pages for AVIC backing pages, it seems to cause VM to slow down quite a bit due to a lot of page faults.
Currently, the AVIC backing pages are acquired from __x86_set_memory region() with APIC_ACCESS_PAGE_PRIVATE_MEMSLOT, which maps the pages for address 0xfee00000 and above for VM to use. I mostly grab this from the VMX implementation in alloc_apic_access_page().
However, the memslot requires specification of the size at the time when calling __x86_set_memory_region(). However, I can't seem to figure out where I can get the number of vcpus at the time when we creating VM. Therefore, I have to track the vcpu creation, and re-acquire larger memslot every time vcpu_create() is called.
I was not sure if this is the right approach, any suggestion for this part.
Thanks, Suravee
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