Re: [PATCH v4 05/37] KVM: x86: hyper-v: Handle HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST{,EX} calls gently

Vitaly Kuznetsov
2022-05-27T11:48:05Z

Yuan Yao <yuan.yao@linux.intel.com> writes:

> On Wed, May 25, 2022 at 11:01:01AM +0200, Vitaly Kuznetsov wrote:
>> Currently, HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST{,EX} calls are handled
>> the exact same way as HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE{,EX}: by
>> flushing the whole VPID and this is sub-optimal. Switch to handling
>> these requests with 'flush_tlb_gva()' hooks instead. Use the newly
>> introduced TLB flush fifo to queue the requests.
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>> arch/x86/kvm/hyperv.c | 102 +++++++++++++++++++++++++++++++++++++-----
>> 1 file changed, 90 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
>> index 762b0b699fdf..576749973727 100644
>> --- a/arch/x86/kvm/hyperv.c
>> +++ b/arch/x86/kvm/hyperv.c
>> @@ -1806,32 +1806,84 @@ static u64 kvm_get_sparse_vp_set(struct kvm *kvm, struct kvm_hv_hcall *hc,
>> sparse_banks, consumed_xmm_halves, offset);
>> }
>>
>> -static void hv_tlb_flush_enqueue(struct kvm_vcpu *vcpu)
>> +static int kvm_hv_get_tlb_flush_entries(struct kvm *kvm, struct kvm_hv_hcall *hc, u64 entries[],
>> + int consumed_xmm_halves, gpa_t offset)
>> +{
>> + return kvm_hv_get_hc_data(kvm, hc, hc->rep_cnt, hc->rep_cnt,
>> + entries, consumed_xmm_halves, offset);
>> +}
>> +
>> +static void hv_tlb_flush_enqueue(struct kvm_vcpu *vcpu, u64 *entries, int count)
>> {
>> struct kvm_vcpu_hv_tlb_flush_fifo *tlb_flush_fifo;
>> struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
>> u64 entry = KVM_HV_TLB_FLUSHALL_ENTRY;
>> + unsigned long flags;
>>
>> if (!hv_vcpu)
>> return;
>>
>> tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
>>
>> - kfifo_in_spinlocked(&tlb_flush_fifo->entries, &entry, 1, &tlb_flush_fifo->write_lock);
>> + spin_lock_irqsave(&tlb_flush_fifo->write_lock, flags);
>> +
>> + /*
>> + * All entries should fit on the fifo leaving one free for 'flush all'
>> + * entry in case another request comes in. In case there's not enough
>> + * space, just put 'flush all' entry there.
>> + */
>> + if (count && entries && count < kfifo_avail(&tlb_flush_fifo->entries)) {
>> + WARN_ON(kfifo_in(&tlb_flush_fifo->entries, entries, count) != count);
>> + goto out_unlock;
>> + }
>> +
>> + /*
>> + * Note: full fifo always contains 'flush all' entry, no need to check the
>> + * return value.
>> + */
>> + kfifo_in(&tlb_flush_fifo->entries, &entry, 1);
>> +
>> +out_unlock:
>> + spin_unlock_irqrestore(&tlb_flush_fifo->write_lock, flags);
>> }
>>
>> void kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu)
>
> Where's the caller to this kvm_hv_vcpu_flush_tlb() ?
> I didn't see th caller in patch 1-22 and remains are
> self-testing patches, any thing I missed ?

No, I screwed up. It was present in
kvm_service_local_tlb_flush_requests() in previous versions but somehow
disappeared. This also means that I haven't tested this properly.

Thanks for catching this! v5 is coming to rescue!

>
>> {
>> struct kvm_vcpu_hv_tlb_flush_fifo *tlb_flush_fifo;
>> struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
>> + u64 entries[KVM_HV_TLB_FLUSH_FIFO_SIZE];
>> + int i, j, count;
>> + gva_t gva;
>>
>> - kvm_vcpu_flush_tlb_guest(vcpu);
>> -
>> - if (!hv_vcpu)
>> + if (!tdp_enabled || !hv_vcpu) {
>> + kvm_vcpu_flush_tlb_guest(vcpu);
>> return;
>> + }
>>
>> tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
>>
>> + count = kfifo_out(&tlb_flush_fifo->entries, entries, KVM_HV_TLB_FLUSH_FIFO_SIZE);
>> +
>> + for (i = 0; i < count; i++) {
>> + if (entries[i] == KVM_HV_TLB_FLUSHALL_ENTRY)
>> + goto out_flush_all;
>> +
>> + /*
>> + * Lower 12 bits of 'address' encode the number of additional
>> + * pages to flush.
>> + */
>> + gva = entries[i] & PAGE_MASK;
>> + for (j = 0; j < (entries[i] & ~PAGE_MASK) + 1; j++)
>> + static_call(kvm_x86_flush_tlb_gva)(vcpu, gva + j * PAGE_SIZE);
>> +
>> + ++vcpu->stat.tlb_flush;
>> + }
>> + goto out_empty_ring;
>> +
>> +out_flush_all:
>> + kvm_vcpu_flush_tlb_guest(vcpu);
>> +
>> +out_empty_ring:
>> kfifo_reset_out(&tlb_flush_fifo->entries);
>> }
>>
>> @@ -1841,11 +1893,21 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>> struct hv_tlb_flush_ex flush_ex;
>> struct hv_tlb_flush flush;
>> DECLARE_BITMAP(vcpu_mask, KVM_MAX_VCPUS);
>> + /*
>> + * Normally, there can be no more than 'KVM_HV_TLB_FLUSH_FIFO_SIZE'
>> + * entries on the TLB flush fifo. The last entry, however, needs to be
>> + * always left free for 'flush all' entry which gets placed when
>> + * there is not enough space to put all the requested entries.
>> + */
>> + u64 __tlb_flush_entries[KVM_HV_TLB_FLUSH_FIFO_SIZE - 1];
>> + u64 *tlb_flush_entries;
>> u64 valid_bank_mask;
>> u64 sparse_banks[KVM_HV_MAX_SPARSE_VCPU_SET_BITS];
>> struct kvm_vcpu *v;
>> unsigned long i;
>> bool all_cpus;
>> + int consumed_xmm_halves = 0;
>> + gpa_t data_offset;
>>
>> /*
>> * The Hyper-V TLFS doesn't allow more than 64 sparse banks, e.g. the
>> @@ -1861,10 +1923,12 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>> flush.address_space = hc->ingpa;
>> flush.flags = hc->outgpa;
>> flush.processor_mask = sse128_lo(hc->xmm[0]);
>> + consumed_xmm_halves = 1;
>> } else {
>> if (unlikely(kvm_read_guest(kvm, hc->ingpa,
>> &flush, sizeof(flush))))
>> return HV_STATUS_INVALID_HYPERCALL_INPUT;
>> + data_offset = sizeof(flush);
>> }
>>
>> trace_kvm_hv_flush_tlb(flush.processor_mask,
>> @@ -1888,10 +1952,12 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>> flush_ex.flags = hc->outgpa;
>> memcpy(&flush_ex.hv_vp_set,
>> &hc->xmm[0], sizeof(hc->xmm[0]));
>> + consumed_xmm_halves = 2;
>> } else {
>> if (unlikely(kvm_read_guest(kvm, hc->ingpa, &flush_ex,
>> sizeof(flush_ex))))
>> return HV_STATUS_INVALID_HYPERCALL_INPUT;
>> + data_offset = sizeof(flush_ex);
>> }
>>
>> trace_kvm_hv_flush_tlb_ex(flush_ex.hv_vp_set.valid_bank_mask,
>> @@ -1907,25 +1973,37 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>> return HV_STATUS_INVALID_HYPERCALL_INPUT;
>>
>> if (all_cpus)
>> - goto do_flush;
>> + goto read_flush_entries;
>>
>> if (!hc->var_cnt)
>> goto ret_success;
>>
>> - if (kvm_get_sparse_vp_set(kvm, hc, sparse_banks, 2,
>> - offsetof(struct hv_tlb_flush_ex,
>> - hv_vp_set.bank_contents)))
>> + if (kvm_get_sparse_vp_set(kvm, hc, sparse_banks, consumed_xmm_halves,
>> + data_offset))
>> + return HV_STATUS_INVALID_HYPERCALL_INPUT;
>> + data_offset += hc->var_cnt * sizeof(sparse_banks[0]);
>> + consumed_xmm_halves += hc->var_cnt;
>> + }
>> +
>> +read_flush_entries:
>> + if (hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE ||
>> + hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX ||
>> + hc->rep_cnt > ARRAY_SIZE(__tlb_flush_entries)) {
>> + tlb_flush_entries = NULL;
>> + } else {
>> + if (kvm_hv_get_tlb_flush_entries(kvm, hc, __tlb_flush_entries,
>> + consumed_xmm_halves, data_offset))
>> return HV_STATUS_INVALID_HYPERCALL_INPUT;
>> + tlb_flush_entries = __tlb_flush_entries;
>> }
>>
>> -do_flush:
>> /*
>> * vcpu->arch.cr3 may not be up-to-date for running vCPUs so we can't
>> * analyze it here, flush TLB regardless of the specified address space.
>> */
>> if (all_cpus) {
>> kvm_for_each_vcpu(i, v, kvm)
>> - hv_tlb_flush_enqueue(v);
>> + hv_tlb_flush_enqueue(v, tlb_flush_entries, hc->rep_cnt);
>>
>> kvm_make_all_cpus_request(kvm, KVM_REQ_HV_TLB_FLUSH);
>> } else {
>> @@ -1935,7 +2013,7 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>> v = kvm_get_vcpu(kvm, i);
>> if (!v)
>> continue;
>> - hv_tlb_flush_enqueue(v);
>> + hv_tlb_flush_enqueue(v, tlb_flush_entries, hc->rep_cnt);
>> }
>>
>> kvm_make_vcpus_request_mask(kvm, KVM_REQ_HV_TLB_FLUSH, vcpu_mask);
>> --
>> 2.35.3
>>
>

--
Vitaly