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    SubjectRe: [PATCH RFC v7 47/64] KVM: SVM: Add support to handle MSR based Page State Change VMGEXIT
    On Wed, Dec 14, 2022 at 01:40:39PM -0600, Michael Roth wrote:
    > From: Brijesh Singh <brijesh.singh@amd.com>
    >
    > SEV-SNP VMs can ask the hypervisor to change the page state in the RMP
    > table to be private or shared using the Page State Change MSR protocol
    > as defined in the GHCB specification.
    >
    > Forward these requests to userspace via KVM_EXIT_VMGEXIT so the VMM can
    > issue the KVM ioctls to update the page state accordingly.
    >
    > Co-developed-by: Michael Roth <michael.roth@amd.com>
    > Signed-off-by: Michael Roth <michael.roth@amd.com>
    > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
    > Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
    > ---
    > arch/x86/include/asm/sev-common.h | 9 ++++++++
    > arch/x86/kvm/svm/sev.c | 25 +++++++++++++++++++++++
    > arch/x86/kvm/trace.h | 34 +++++++++++++++++++++++++++++++
    > arch/x86/kvm/x86.c | 1 +
    > 4 files changed, 69 insertions(+)
    >
    > diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
    > index 0a9055cdfae2..ee38f7408470 100644
    > --- a/arch/x86/include/asm/sev-common.h
    > +++ b/arch/x86/include/asm/sev-common.h
    > @@ -93,6 +93,10 @@ enum psc_op {
    > };
    >
    > #define GHCB_MSR_PSC_REQ 0x014
    > +#define GHCB_MSR_PSC_GFN_POS 12
    > +#define GHCB_MSR_PSC_GFN_MASK GENMASK_ULL(39, 0)
    > +#define GHCB_MSR_PSC_OP_POS 52
    > +#define GHCB_MSR_PSC_OP_MASK 0xf
    > #define GHCB_MSR_PSC_REQ_GFN(gfn, op) \
    > /* GHCBData[55:52] */ \
    > (((u64)((op) & 0xf) << 52) | \
    > @@ -102,6 +106,11 @@ enum psc_op {
    > GHCB_MSR_PSC_REQ)
    >
    > #define GHCB_MSR_PSC_RESP 0x015
    > +#define GHCB_MSR_PSC_ERROR_POS 32
    > +#define GHCB_MSR_PSC_ERROR_MASK GENMASK_ULL(31, 0)
    > +#define GHCB_MSR_PSC_ERROR GENMASK_ULL(31, 0)
    > +#define GHCB_MSR_PSC_RSVD_POS 12
    > +#define GHCB_MSR_PSC_RSVD_MASK GENMASK_ULL(19, 0)
    > #define GHCB_MSR_PSC_RESP_VAL(val) \
    > /* GHCBData[63:32] */ \
    > (((u64)(val) & GENMASK_ULL(63, 32)) >> 32)
    > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
    > index d7b467b620aa..d7988629073b 100644
    > --- a/arch/x86/kvm/svm/sev.c
    > +++ b/arch/x86/kvm/svm/sev.c
    > @@ -29,6 +29,7 @@
    > #include "svm_ops.h"
    > #include "cpuid.h"
    > #include "trace.h"
    > +#include "mmu.h"
    >
    > #ifndef CONFIG_KVM_AMD_SEV
    > /*
    > @@ -3350,6 +3351,23 @@ static void set_ghcb_msr(struct vcpu_svm *svm, u64 value)
    > svm->vmcb->control.ghcb_gpa = value;
    > }
    >
    > +/*
    > + * TODO: need to get the value set by userspace in vcpu->run->vmgexit.ghcb_msr
    > + * and process that here accordingly.
    > + */
    > +static int snp_complete_psc_msr_protocol(struct kvm_vcpu *vcpu)
    > +{
    > + struct vcpu_svm *svm = to_svm(vcpu);
    > +
    > + set_ghcb_msr_bits(svm, 0,
    > + GHCB_MSR_PSC_ERROR_MASK, GHCB_MSR_PSC_ERROR_POS);
    > +
    > + set_ghcb_msr_bits(svm, 0, GHCB_MSR_PSC_RSVD_MASK, GHCB_MSR_PSC_RSVD_POS);
    > + set_ghcb_msr_bits(svm, GHCB_MSR_PSC_RESP, GHCB_MSR_INFO_MASK, GHCB_MSR_INFO_POS);
    > +
    > + return 1; /* resume */
    > +}
    > +
    > static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
    > {
    > struct vmcb_control_area *control = &svm->vmcb->control;
    > @@ -3450,6 +3468,13 @@ static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
    > GHCB_MSR_INFO_POS);
    > break;
    > }
    > + case GHCB_MSR_PSC_REQ:
    > + vcpu->run->exit_reason = KVM_EXIT_VMGEXIT;
    > + vcpu->run->vmgexit.ghcb_msr = control->ghcb_gpa;
    > + vcpu->arch.complete_userspace_io = snp_complete_psc_msr_protocol;
    > +
    > + ret = -1;
    > + break;

    What's the reasoning behind returning an error (-1) here? This error bubbles all
    the way up to the `KVM_RUN` ioctl. Would it be more appropriate to return 0?
    Returning 0 would cause a VM exit without indicating an error to userspace.

    > case GHCB_MSR_TERM_REQ: {
    > u64 reason_set, reason_code;
    >
    > diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
    > index 83843379813e..65861d2d086c 100644
    > --- a/arch/x86/kvm/trace.h
    > +++ b/arch/x86/kvm/trace.h
    > @@ -7,6 +7,7 @@
    > #include <asm/svm.h>
    > #include <asm/clocksource.h>
    > #include <asm/pvclock-abi.h>
    > +#include <asm/sev-common.h>
    >
    > #undef TRACE_SYSTEM
    > #define TRACE_SYSTEM kvm
    > @@ -1831,6 +1832,39 @@ TRACE_EVENT(kvm_vmgexit_msr_protocol_exit,
    > __entry->vcpu_id, __entry->ghcb_gpa, __entry->result)
    > );
    >
    > +/*
    > + * Tracepoint for the SEV-SNP page state change processing
    > + */
    > +#define psc_operation \
    > + {SNP_PAGE_STATE_PRIVATE, "private"}, \
    > + {SNP_PAGE_STATE_SHARED, "shared"} \
    > +
    > +TRACE_EVENT(kvm_snp_psc,
    > + TP_PROTO(unsigned int vcpu_id, u64 pfn, u64 gpa, u8 op, int level),
    > + TP_ARGS(vcpu_id, pfn, gpa, op, level),
    > +
    > + TP_STRUCT__entry(
    > + __field(int, vcpu_id)
    > + __field(u64, pfn)
    > + __field(u64, gpa)
    > + __field(u8, op)
    > + __field(int, level)
    > + ),
    > +
    > + TP_fast_assign(
    > + __entry->vcpu_id = vcpu_id;
    > + __entry->pfn = pfn;
    > + __entry->gpa = gpa;
    > + __entry->op = op;
    > + __entry->level = level;
    > + ),
    > +
    > + TP_printk("vcpu %u, pfn %llx, gpa %llx, op %s, level %d",
    > + __entry->vcpu_id, __entry->pfn, __entry->gpa,
    > + __print_symbolic(__entry->op, psc_operation),
    > + __entry->level)
    > +);
    > +
    > #endif /* _TRACE_KVM_H */
    >
    > #undef TRACE_INCLUDE_PATH
    > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    > index 732f9cbbadb5..08dd1ef7e136 100644
    > --- a/arch/x86/kvm/x86.c
    > +++ b/arch/x86/kvm/x86.c
    > @@ -13481,6 +13481,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_vmgexit_enter);
    > EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_vmgexit_exit);
    > EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_vmgexit_msr_protocol_enter);
    > EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_vmgexit_msr_protocol_exit);
    > +EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_snp_psc);
    >
    > static int __init kvm_x86_init(void)
    > {
    > --
    > 2.25.1
    >

    Regards, Tom

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