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Date: Thu, 7 Apr 2022 17:33:00 +0000
From: Sean Christopherson <seanjc@...gle.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Michael Kelley <mikelley@...rosoft.com>,
Siddharth Chandrasekaran <sidcha@...zon.de>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 03/31] KVM: x86: hyper-v: Handle
HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST{,EX} calls gently
On Thu, Apr 07, 2022, 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 ring to queue the requests.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
> arch/x86/kvm/hyperv.c | 141 ++++++++++++++++++++++++++++++++++++------
> 1 file changed, 121 insertions(+), 20 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 81c44e0eadf9..a54d41656f30 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1792,6 +1792,35 @@ static u64 kvm_get_sparse_vp_set(struct kvm *kvm, struct kvm_hv_hcall *hc,
> var_cnt * sizeof(*sparse_banks));
> }
>
> +static int kvm_hv_get_tlbflush_entries(struct kvm *kvm, struct kvm_hv_hcall *hc, u64 entries[],
> + u32 data_offset, int consumed_xmm_halves)
data_offset should be gpa_t, and the order of params should be consistent between
this and kvm_get_sparse_vp_set().
> +{
> + int i;
> +
> + if (hc->fast) {
> + /*
> + * Each XMM holds two entries, but do not count halves that
> + * have already been consumed.
> + */
> + if (hc->rep_cnt > (2 * HV_HYPERCALL_MAX_XMM_REGISTERS - consumed_xmm_halves))
> + return -EINVAL;
> +
> + for (i = 0; i < hc->rep_cnt; i++) {
> + int j = i + consumed_xmm_halves;
> +
> + if (j % 2)
> + entries[i] = sse128_hi(hc->xmm[j / 2]);
> + else
> + entries[i] = sse128_lo(hc->xmm[j / 2]);
> + }
> +
> + return 0;
> + }
> +
> + return kvm_read_guest(kvm, hc->ingpa + data_offset,
> + entries, hc->rep_cnt * sizeof(entries[0]));
This is almost verbatim copy+pasted from kvm_get_sparse_vp_set(). If you slot in
the attached patched before this, then this function becomes:
static int kvm_hv_get_tlbflush_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);
}
> +}
...
> @@ -1840,15 +1891,47 @@ void kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu)
> {
> struct kvm_vcpu_hv_tlbflush_ring *tlb_flush_ring;
> struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> -
> - kvm_vcpu_flush_tlb_guest(vcpu);
> -
> - if (!hv_vcpu)
> + struct kvm_vcpu_hv_tlbflush_entry *entry;
> + int read_idx, write_idx;
> + u64 address;
> + u32 count;
> + int i, j;
> +
> + if (!tdp_enabled || !hv_vcpu) {
> + kvm_vcpu_flush_tlb_guest(vcpu);
> return;
> + }
>
> tlb_flush_ring = &hv_vcpu->tlb_flush_ring;
> + read_idx = READ_ONCE(tlb_flush_ring->read_idx);
> + write_idx = READ_ONCE(tlb_flush_ring->write_idx);
> +
> + /* Pairs with smp_wmb() in hv_tlb_flush_ring_enqueue() */
> + smp_rmb();
>
> - tlb_flush_ring->read_idx = tlb_flush_ring->write_idx;
> + for (i = read_idx; i != write_idx; i = (i + 1) % KVM_HV_TLB_FLUSH_RING_SIZE) {
> + entry = &tlb_flush_ring->entries[i];
> +
> + if (entry->flush_all)
> + goto out_flush_all;
> +
> + /*
> + * Lower 12 bits of 'address' encode the number of additional
> + * pages to flush.
> + */
> + address = entry->addr & PAGE_MASK;
> + count = (entry->addr & ~PAGE_MASK) + 1;
> + for (j = 0; j < count; j++)
> + static_call(kvm_x86_flush_tlb_gva)(vcpu, address + j * PAGE_SIZE);
> + }
> + ++vcpu->stat.tlb_flush;
> + goto out_empty_ring;
> +
> +out_flush_all:
> + kvm_vcpu_flush_tlb_guest(vcpu);
> +
> +out_empty_ring:
> + tlb_flush_ring->read_idx = write_idx;
> }
>
> static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
> @@ -1857,12 +1940,13 @@ 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);
> + u64 entries[KVM_HV_TLB_FLUSH_RING_SIZE - 2];
What's up with the -2? And given the multitude of things going on in this code,
I'd strongly prefer this be tlbflush_entries.
Actually, if you do:
u64 __tlbflush_entries[KVM_HV_TLB_FLUSH_RING_SIZE - 2];
u64 *tlbflush_entries;
and drop all_addr, the code to get entries can be
if (hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE ||
hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX ||
hc->rep_cnt > ARRAY_SIZE(tlbflush_entries)) {
tlbfluish_entries = NULL;
} else {
if (kvm_hv_get_tlbflush_entries(kvm, hc, __tlbflush_entries,
consumed_xmm_halves, data_offset))
return HV_STATUS_INVALID_HYPERCALL_INPUT;
tlbfluish_entries = __tlbflush_entries;
}
and the calls to queue flushes becomes
hv_tlb_flush_ring_enqueue(v, tlbflush_entries, hc->rep_cnt);
That way a bug will "just" be a NULL pointer dereference and not consumption of
uninitialized data (though such a bug might be caught be caught by the compiler).
> u64 valid_bank_mask;
> u64 sparse_banks[KVM_HV_MAX_SPARSE_VCPU_SET_BITS];
> struct kvm_vcpu *v;
> unsigned long i;
> - bool all_cpus;
> -
> + bool all_cpus, all_addr;
> + int data_offset = 0, consumed_xmm_halves = 0;
data_offset should be a gpa_t.
> /*
> * The Hyper-V TLFS doesn't allow more than 64 sparse banks, e.g. the
> * valid mask is a u64. Fail the build if KVM's max allowed number of
...
> +read_flush_entries:
> + if (hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE ||
> + hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX ||
> + hc->rep_cnt > (KVM_HV_TLB_FLUSH_RING_SIZE - 2)) {
Rather than duplicate the -2 magic, it's far better to do:
> + all_addr = true;
> + } else {
> + if (kvm_hv_get_tlbflush_entries(kvm, hc, entries,
> + data_offset, consumed_xmm_halves))
As mentioned, the order for this call should match kvm_get_sparse_vp_set().
> return HV_STATUS_INVALID_HYPERCALL_INPUT;
> + all_addr = false;
> }
>
> -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_ring_enqueue(v);
> + hv_tlb_flush_ring_enqueue(v, all_addr, entries, hc->rep_cnt);
>
> kvm_make_all_cpus_request(kvm, KVM_REQ_HV_TLB_FLUSH);
> } else {
> @@ -1951,7 +2052,7 @@ 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_ring_enqueue(v);
> + hv_tlb_flush_ring_enqueue(v, all_addr, entries, hc->rep_cnt);
> }
>
> kvm_make_vcpus_request_mask(kvm, KVM_REQ_HV_TLB_FLUSH, vcpu_mask);
> --
> 2.35.1
>
View attachment "0001-KVM-x86-hyper-v-Add-helper-to-read-hypercall-data-fo.patch" of type "text/x-diff" (4045 bytes)
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