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Message-ID: <Y77J7C2E9Xd1QcmZ@notebook>
Date: Wed, 11 Jan 2023 15:38:36 +0100
From: Tom Dohrmann <erbse.13@....de>
To: Michael Roth <michael.roth@....com>
Cc: kvm@...r.kernel.org, linux-coco@...ts.linux.dev,
linux-mm@...ck.org, linux-crypto@...r.kernel.org, x86@...nel.org,
linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
luto@...nel.org, dave.hansen@...ux.intel.com, slp@...hat.com,
pgonda@...gle.com, peterz@...radead.org,
srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com,
dovmurik@...ux.ibm.com, tobin@....com, bp@...en8.de,
vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
tony.luck@...el.com, marcorr@...gle.com,
sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
dgilbert@...hat.com, jarkko@...nel.org, ashish.kalra@....com,
harald@...fian.com, Brijesh Singh <brijesh.singh@....com>
Subject: Re: [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@....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@....com>
> Signed-off-by: Michael Roth <michael.roth@....com>
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> Signed-off-by: Ashish Kalra <ashish.kalra@....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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