Re: [PATCH v2 3/4] KVM: x86: kvm_hv_flush_tlb use inputs from XMM registers

Siddharth Chandrasekaran
2021-04-13T21:08:29Z

On Tue, Apr 13, 2021 at 04:09:48PM +0200, Vitaly Kuznetsov wrote:
> Siddharth Chandrasekaran <sidcha@amazon.de> writes:
> > Hyper-V supports the use of XMM registers to perform fast hypercalls.
> > This allows guests to take advantage of the improved performance of the
> > fast hypercall interface even though a hypercall may require more than
> > (the current maximum of) two input registers.
> >
> > The XMM fast hypercall interface uses six additional XMM registers (XMM0
> > to XMM5) to allow the guest to pass an input parameter block of up to
> > 112 bytes. Hyper-V can also return data back to the guest in the
> > remaining XMM registers that are not used by the current hypercall.
> >
> > Add framework to read/write to XMM registers in kvm_hv_hypercall() and
> > use the additional hypercall inputs from XMM registers in
> > kvm_hv_flush_tlb() when possible.
> >
> > Cc: Alexander Graf <graf@amazon.com>
> > Co-developed-by: Evgeny Iakovlev <eyakovl@amazon.de>
> > Signed-off-by: Evgeny Iakovlev <eyakovl@amazon.de>
> > Signed-off-by: Siddharth Chandrasekaran <sidcha@amazon.de>
> > ---
> > arch/x86/kvm/hyperv.c | 109 ++++++++++++++++++++++++++++++++++--------
> > 1 file changed, 90 insertions(+), 19 deletions(-)
> >
> > diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> > index 8f6babd1ea0d..1f9959aba70d 100644
> > --- a/arch/x86/kvm/hyperv.c
> > +++ b/arch/x86/kvm/hyperv.c
> > @@ -36,6 +36,7 @@
> >
> > #include "trace.h"
> > #include "irq.h"
> > +#include "fpu.h"
> >
> > /* "Hv#1" signature */
> > #define HYPERV_CPUID_SIGNATURE_EAX 0x31237648
> > @@ -1623,6 +1624,8 @@ static __always_inline unsigned long *sparse_set_to_vcpu_mask(
> > return vcpu_bitmap;
> > }
> >
> > +#define KVM_HV_HYPERCALL_MAX_XMM_REGISTERS 6
>
> Nitpick: this is not KVM-specific so could probably go to arch/x86/include/asm/hyperv-tlfs.h

Ack.

> > +
> > struct kvm_hv_hcall {
> > u64 param;
> > u64 ingpa;
> > @@ -1632,10 +1635,14 @@ struct kvm_hv_hcall {
> > u16 rep_idx;
> > bool fast;
> > bool rep;
> > + sse128_t xmm[KVM_HV_HYPERCALL_MAX_XMM_REGISTERS];
> > + bool xmm_dirty;
> > };
> >
> > static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool ex)
> > {
> > + int i, j;
> > + gpa_t gpa;
> > struct kvm *kvm = vcpu->kvm;
> > struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> > struct hv_tlb_flush_ex flush_ex;
> > @@ -1649,8 +1656,15 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
> > bool all_cpus;
> >
> > if (!ex) {
> > - if (unlikely(kvm_read_guest(kvm, hc->ingpa, &flush, sizeof(flush))))
> > - return HV_STATUS_INVALID_HYPERCALL_INPUT;
> > + if (hc->fast) {
> > + flush.address_space = hc->ingpa;
> > + flush.flags = hc->outgpa;
> > + flush.processor_mask = sse128_lo(hc->xmm[0]);
> > + } else {
> > + if (unlikely(kvm_read_guest(kvm, hc->ingpa,
> > + &flush, sizeof(flush))))
> > + return HV_STATUS_INVALID_HYPERCALL_INPUT;
> > + }
> >
> > trace_kvm_hv_flush_tlb(flush.processor_mask,
> > flush.address_space, flush.flags);
> > @@ -1668,9 +1682,16 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
> > all_cpus = (flush.flags & HV_FLUSH_ALL_PROCESSORS) ||
> > flush.processor_mask == 0;
> > } else {
> > - if (unlikely(kvm_read_guest(kvm, hc->ingpa, &flush_ex,
> > - sizeof(flush_ex))))
> > - return HV_STATUS_INVALID_HYPERCALL_INPUT;
> > + if (hc->fast) {
> > + flush_ex.address_space = hc->ingpa;
> > + flush_ex.flags = hc->outgpa;
> > + memcpy(&flush_ex.hv_vp_set,
> > + &hc->xmm[0], sizeof(hc->xmm[0]));
> > + } else {
> > + if (unlikely(kvm_read_guest(kvm, hc->ingpa, &flush_ex,
> > + sizeof(flush_ex))))
> > + return HV_STATUS_INVALID_HYPERCALL_INPUT;
> > + }
> >
> > trace_kvm_hv_flush_tlb_ex(flush_ex.hv_vp_set.valid_bank_mask,
> > flush_ex.hv_vp_set.format,
> > @@ -1681,20 +1702,29 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
> > all_cpus = flush_ex.hv_vp_set.format !=
> > HV_GENERIC_SET_SPARSE_4K;
> >
> > - sparse_banks_len =
> > - bitmap_weight((unsigned long *)&valid_bank_mask, 64) *
> > - sizeof(sparse_banks[0]);
> > + sparse_banks_len = bitmap_weight((unsigned long *)&valid_bank_mask, 64);
> >
> > if (!sparse_banks_len && !all_cpus)
> > goto ret_success;
> >
> > - if (!all_cpus &&
> > - kvm_read_guest(kvm,
> > - hc->ingpa + offsetof(struct hv_tlb_flush_ex,
> > - hv_vp_set.bank_contents),
> > - sparse_banks,
> > - sparse_banks_len))
> > - return HV_STATUS_INVALID_HYPERCALL_INPUT;
> > + if (!all_cpus) {
> > + if (hc->fast) {
> > + if (sparse_banks_len > KVM_HV_HYPERCALL_MAX_XMM_REGISTERS - 1)
> > + return HV_STATUS_INVALID_HYPERCALL_INPUT;
> > + for (i = 0, j = 1; i < sparse_banks_len; i += 2, j++) {
>
> Nitpick: you don't really need 'j' here as 'j == i/2 + 1', right?

Yes, you are right. Changed.

> > + sparse_banks[i + 0] = sse128_lo(hc->xmm[j]);
>
> Using ' + 0' for identation is ... unusual :-) I'm not opposed to it
> here though.

Old habit :-).

> > + sparse_banks[i + 1] = sse128_hi(hc->xmm[j]);
> > + }
> > + } else {
> > + gpa = hc->ingpa;
> > + gpa += offsetof(struct hv_tlb_flush_ex,
> > + hv_vp_set.bank_contents);
>
> Nitpick: if splitting these into two lines is only done to fit into 80
> chars then I'd the requirement is no more so we can be a bit wider.
>
> gpa = hc->ingpa + offsetof(...)

Ack.

> > + if (unlikely(kvm_read_guest(kvm, gpa, sparse_banks,
> > + sparse_banks_len *
> > + sizeof(sparse_banks[0]))))
> > + return HV_STATUS_INVALID_HYPERCALL_INPUT;
> > + }
> > + }
> > }
> >
> > cpumask_clear(&hv_vcpu->tlb_flush);
> > @@ -1890,6 +1920,41 @@ static u16 kvm_hvcall_signal_event(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *h
> > return HV_STATUS_SUCCESS;
> > }
> >
> > +static bool is_xmm_fast_hypercall(struct kvm_hv_hcall *hc)
> > +{
> > + switch (hc->code) {
> > + case HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST:
> > + case HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE:
> > + case HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX:
> > + case HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX:
> > + return true;
> > + }
> > +
> > + return false;
> > +}
> > +
> > +static inline void kvm_hv_hypercall_read_xmm(struct kvm_hv_hcall *hc)
> > +{
> > + int reg;
> > +
> > + kvm_fpu_get();
> > + for (reg = 0; reg < KVM_HV_HYPERCALL_MAX_XMM_REGISTERS; reg++)
> > + _kvm_read_sse_reg(reg, &hc->xmm[reg]);
> > + kvm_fpu_put();
> > + hc->xmm_dirty = false;
> > +}
> > +
> > +static inline void kvm_hv_hypercall_write_xmm(struct kvm_hv_hcall *hc)
> > +{
> > + int reg;
> > +
> > + kvm_fpu_get();
> > + for (reg = 0; reg < KVM_HV_HYPERCALL_MAX_XMM_REGISTERS; reg++)
> > + _kvm_write_sse_reg(reg, &hc->xmm[reg]);
> > + kvm_fpu_put();
> > + hc->xmm_dirty = false;
> > +}
> > +
> > int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> > {
> > struct kvm_hv_hcall hc;
> > @@ -1926,6 +1991,9 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> > hc.rep_idx = (hc.param >> HV_HYPERCALL_REP_START_OFFSET) & 0xfff;
> > hc.rep = !!(hc.rep_cnt || hc.rep_idx);
> >
> > + if (hc.fast && is_xmm_fast_hypercall(&hc))
> > + kvm_hv_hypercall_read_xmm(&hc);
> > +
> > trace_kvm_hv_hypercall(hc.code, hc.fast, hc.rep_cnt, hc.rep_idx,
> > hc.ingpa, hc.outgpa);
> >
> > @@ -1961,28 +2029,28 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> > kvm_hv_hypercall_complete_userspace;
> > return 0;
> > case HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST:
> > - if (unlikely(hc.fast || !hc.rep_cnt || hc.rep_idx)) {
> > + if (unlikely(!hc.rep_cnt || hc.rep_idx)) {
> > ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> > break;
> > }
> > ret = kvm_hv_flush_tlb(vcpu, &hc, false);
> > break;
> > case HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE:
> > - if (unlikely(hc.fast || hc.rep)) {
> > + if (unlikely(hc.rep)) {
> > ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> > break;
> > }
> > ret = kvm_hv_flush_tlb(vcpu, &hc, false);
> > break;
> > case HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX:
> > - if (unlikely(hc.fast || !hc.rep_cnt || hc.rep_idx)) {
> > + if (unlikely(!hc.rep_cnt || hc.rep_idx)) {
> > ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> > break;
> > }
> > ret = kvm_hv_flush_tlb(vcpu, &hc, true);
> > break;
> > case HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX:
> > - if (unlikely(hc.fast || hc.rep)) {
> > + if (unlikely(hc.rep)) {
> > ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> > break;
> > }
> > @@ -2035,6 +2103,9 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> > break;
> > }
> >
> > + if (hc.xmm_dirty)
> > + kvm_hv_hypercall_write_xmm(&hc);
> > +
>
> Wei already mention that but as 'xmm_dirty' is not being used in this
> patch I'd suggest we move it out too.

Okay, I should remove HV_X64_HYPERCALL_XMM_OUTPUT_AVAILABLE for now then.

~ Sid.