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Message-ID: <e85fb226e28ada35efe9abd208ddb60d92e9f14c.camel@redhat.com>
Date: Tue, 28 Nov 2023 08:57:27 +0200
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Alexander Graf <graf@...zon.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Nicolas Saenz Julienne <nsaenz@...zon.com>,
kvm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
pbonzini@...hat.com, seanjc@...gle.com, anelkz@...zon.com,
dwmw@...zon.co.uk, jgowans@...zon.com, corbert@....net,
kys@...rosoft.com, haiyangz@...rosoft.com, decui@...rosoft.com,
x86@...nel.org, linux-doc@...r.kernel.org
Subject: Re: [RFC 03/33] KVM: x86: hyper-v: Introduce XMM output support
On Wed, 2023-11-08 at 13:16 +0100, Alexander Graf wrote:
> On 08.11.23 13:11, Vitaly Kuznetsov wrote:
> > Alexander Graf <graf@...zon.com> writes:
> >
> > > On 08.11.23 12:17, Nicolas Saenz Julienne wrote:
> > > > Prepare infrastructure to be able to return data through the XMM
> > > > registers when Hyper-V hypercalls are issues in fast mode. The XMM
> > > > registers are exposed to user-space through KVM_EXIT_HYPERV_HCALL and
> > > > restored on successful hypercall completion.
> > > >
> > > > Signed-off-by: Nicolas Saenz Julienne <nsaenz@...zon.com>
> > > > ---
> > > > arch/x86/include/asm/hyperv-tlfs.h | 2 +-
> > > > arch/x86/kvm/hyperv.c | 33 +++++++++++++++++++++++++++++-
> > > > include/uapi/linux/kvm.h | 6 ++++++
> > > > 3 files changed, 39 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> > > > index 2ff26f53cd62..af594aa65307 100644
> > > > --- a/arch/x86/include/asm/hyperv-tlfs.h
> > > > +++ b/arch/x86/include/asm/hyperv-tlfs.h
> > > > @@ -49,7 +49,7 @@
> > > > /* Support for physical CPU dynamic partitioning events is available*/
> > > > #define HV_X64_CPU_DYNAMIC_PARTITIONING_AVAILABLE BIT(3)
> > > > /*
> > > > - * Support for passing hypercall input parameter block via XMM
> > > > + * Support for passing hypercall input and output parameter block via XMM
> > > > * registers is available
> > > > */
> > > > #define HV_X64_HYPERCALL_XMM_INPUT_AVAILABLE BIT(4)
> > > > diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> > > > index 238afd7335e4..e1bc861ab3b0 100644
> > > > --- a/arch/x86/kvm/hyperv.c
> > > > +++ b/arch/x86/kvm/hyperv.c
> > > > @@ -1815,6 +1815,7 @@ struct kvm_hv_hcall {
> > > > u16 rep_idx;
> > > > bool fast;
> > > > bool rep;
> > > > + bool xmm_dirty;
> > > > sse128_t xmm[HV_HYPERCALL_MAX_XMM_REGISTERS];
> > > >
> > > > /*
> > > > @@ -2346,9 +2347,33 @@ static int kvm_hv_hypercall_complete(struct kvm_vcpu *vcpu, u64 result)
> > > > return ret;
> > > > }
> > > >
> > > > +static void kvm_hv_write_xmm(struct kvm_hyperv_xmm_reg *xmm)
> > > > +{
> > > > + int reg;
> > > > +
> > > > + kvm_fpu_get();
> > > > + for (reg = 0; reg < HV_HYPERCALL_MAX_XMM_REGISTERS; reg++) {
> > > > + const sse128_t data = sse128(xmm[reg].low, xmm[reg].high);
> > > > + _kvm_write_sse_reg(reg, &data);
> > > > + }
> > > > + kvm_fpu_put();
> > > > +}
> > > > +
> > > > +static bool kvm_hv_is_xmm_output_hcall(u16 code)
> > > > +{
> > > > + return false;
> > > > +}
> > > > +
> > > > static int kvm_hv_hypercall_complete_userspace(struct kvm_vcpu *vcpu)
> > > > {
> > > > - return kvm_hv_hypercall_complete(vcpu, vcpu->run->hyperv.u.hcall.result);
> > > > + bool fast = !!(vcpu->run->hyperv.u.hcall.input & HV_HYPERCALL_FAST_BIT);
> > > > + u16 code = vcpu->run->hyperv.u.hcall.input & 0xffff;
> > > > + u64 result = vcpu->run->hyperv.u.hcall.result;
> > > > +
> > > > + if (kvm_hv_is_xmm_output_hcall(code) && hv_result_success(result) && fast)
> > > > + kvm_hv_write_xmm(vcpu->run->hyperv.u.hcall.xmm);
> > > > +
> > > > + return kvm_hv_hypercall_complete(vcpu, result);
> > > > }
> > > >
> > > > static u16 kvm_hvcall_signal_event(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
> > > > @@ -2623,6 +2648,9 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> > > > break;
> > > > }
> > > >
> > > > + if ((ret & HV_HYPERCALL_RESULT_MASK) == HV_STATUS_SUCCESS && hc.xmm_dirty)
> > > > + kvm_hv_write_xmm((struct kvm_hyperv_xmm_reg*)hc.xmm);
> > > > +
> > > > hypercall_complete:
> > > > return kvm_hv_hypercall_complete(vcpu, ret);
> > > >
> > > > @@ -2632,6 +2660,8 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> > > > vcpu->run->hyperv.u.hcall.input = hc.param;
> > > > vcpu->run->hyperv.u.hcall.params[0] = hc.ingpa;
> > > > vcpu->run->hyperv.u.hcall.params[1] = hc.outgpa;
> > > > + if (hc.fast)
> > > > + memcpy(vcpu->run->hyperv.u.hcall.xmm, hc.xmm, sizeof(hc.xmm));
> > > > vcpu->arch.complete_userspace_io = kvm_hv_hypercall_complete_userspace;
> > > > return 0;
> > > > }
> > > > @@ -2780,6 +2810,7 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
> > > > ent->ebx |= HV_ENABLE_EXTENDED_HYPERCALLS;
> > > >
> > > > ent->edx |= HV_X64_HYPERCALL_XMM_INPUT_AVAILABLE;
> > > > + ent->edx |= HV_X64_HYPERCALL_XMM_OUTPUT_AVAILABLE;
> > >
> > > Shouldn't this be guarded by an ENABLE_CAP to make sure old user space
> > > that doesn't know about xmm outputs is still able to run with newer kernels?
> > >
> > No, we don't do CAPs for new Hyper-V features anymore since we have
> > KVM_GET_SUPPORTED_HV_CPUID. Userspace is not supposed to simply copy
> > its output into guest visible CPUIDs, it must only enable features it
> > knows. Even 'hv_passthrough' option in QEMU doesn't pass unknown
> > features through.
>
> Ah, nice :). That simplifies things.
>
>
> Alex
Besides other remarks I think that this patch is reasonable,
and maybe it can be queued before the main VSM series,
assuming that it comes with a unit test to avoid having
dead code in the kernel.
Best regards,
Maxim Levitsky
>
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