Re: [PATCH RFC v8 34/56] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START command

From: Zhi Wang
Date: Thu Feb 23 2023 - 16:41:22 EST

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On Mon, 20 Feb 2023 12:38:25 -0600
Michael Roth <michael.roth@xxxxxxx> wrote:

> From: Brijesh Singh <brijesh.singh@xxxxxxx>
>
> KVM_SEV_SNP_LAUNCH_START begins the launch process for an SEV-SNP guest.
> The command initializes a cryptographic digest context used to construct
> the measurement of the guest. If the guest is expected to be migrated,
> the command also binds a migration agent (MA) to the guest.
>
> For more information see the SEV-SNP specification.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
> ---
> .../virt/kvm/x86/amd-memory-encryption.rst | 24 ++++
> arch/x86/kvm/svm/sev.c | 121 +++++++++++++++++-
> arch/x86/kvm/svm/svm.h | 1 +
> include/uapi/linux/kvm.h | 10 ++
> 4 files changed, 153 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/virt/kvm/x86/amd-memory-encryption.rst b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
> index 2432213bd0ea..58971fc02a15 100644
> --- a/Documentation/virt/kvm/x86/amd-memory-encryption.rst
> +++ b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
> @@ -461,6 +461,30 @@ The flags bitmap is defined as::
> If the specified flags is not supported then return -EOPNOTSUPP, and the supported
> flags are returned.
>
> +19. KVM_SNP_LAUNCH_START
> +------------------------
> +
> +The KVM_SNP_LAUNCH_START command is used for creating the memory encryption
> +context for the SEV-SNP guest. To create the encryption context, user must
> +provide a guest policy, migration agent (if any) and guest OS visible
> +workarounds value as defined SEV-SNP specification.
> +
> +Parameters (in): struct kvm_snp_launch_start
> +
> +Returns: 0 on success, -negative on error
> +
> +::
> +
> + struct kvm_sev_snp_launch_start {
> + __u64 policy; /* Guest policy to use. */
> + __u64 ma_uaddr; /* userspace address of migration agent */
> + __u8 ma_en; /* 1 if the migration agent is enabled */
> + __u8 imi_en; /* set IMI to 1. */
> + __u8 gosvw[16]; /* guest OS visible workarounds */
> + };
> +
> +See the SEV-SNP specification for further detail on the launch input.
> +
> References
> ==========
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index a8efe1f6bf77..097bb2138360 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -22,6 +22,7 @@
> #include <asm/pkru.h>
> #include <asm/trapnr.h>
> #include <asm/fpu/xcr.h>
> +#include <asm/sev.h>
>
> #include "mmu.h"
> #include "x86.h"
> @@ -75,6 +76,8 @@ static unsigned int nr_asids;
> static unsigned long *sev_asid_bitmap;
> static unsigned long *sev_reclaim_asid_bitmap;
>
> +static int snp_decommission_context(struct kvm *kvm);
> +
> struct enc_region {
> struct list_head list;
> unsigned long npages;
> @@ -100,12 +103,17 @@ static int sev_flush_asids(int min_asid, int max_asid)
> down_write(&sev_deactivate_lock);
>
> wbinvd_on_all_cpus();
> - ret = sev_guest_df_flush(&error);
> +
> + if (sev_snp_enabled)
> + ret = sev_do_cmd(SEV_CMD_SNP_DF_FLUSH, NULL, &error);
> + else
> + ret = sev_guest_df_flush(&error);
>
> up_write(&sev_deactivate_lock);
>
> if (ret)
> - pr_err("SEV: DF_FLUSH failed, ret=%d, error=%#x\n", ret, error);
> + pr_err("SEV%s: DF_FLUSH failed, ret=%d, error=%#x\n",
> + sev_snp_enabled ? "-SNP" : "", ret, error);
>
> return ret;
> }
> @@ -2011,6 +2019,80 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, unsigned int source_fd)
> return ret;
> }
>
> +/*
> + * The guest context contains all the information, keys and metadata
> + * associated with the guest that the firmware tracks to implement SEV
> + * and SNP features. The firmware stores the guest context in hypervisor
> + * provide page via the SNP_GCTX_CREATE command.
> + */
> +static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> + struct sev_data_snp_addr data = {};
> + void *context;
> + int rc;
> +
> + /* Allocate memory for context page */
> + context = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT);
> + if (!context)
> + return NULL;
> +
> + data.gctx_paddr = __psp_pa(context);
> + rc = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_GCTX_CREATE, &data, &argp->error);
> + if (rc) {
> + snp_free_firmware_page(context);
> + return NULL;
> + }
> +
> + return context;
> +}
> +
> +static int snp_bind_asid(struct kvm *kvm, int *error)
> +{
> + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> + struct sev_data_snp_activate data = {0};
> +
> + data.gctx_paddr = __psp_pa(sev->snp_context);
> + data.asid = sev_get_asid(kvm);
> + return sev_issue_cmd(kvm, SEV_CMD_SNP_ACTIVATE, &data, error);

According to the SNP ABI specification[1] 8.10 SNP_ACTIVATE:

"The firmware checks that a DF_FLUSH is not required. If a DF_FLUSH is
required, the firmware returns DFFLUSH_REQUIRED. Note that all ASIDs are
marked to require a DF_FLUSH at reset."

Do we need a SNP_DF_FLUSH here before calling SNP_ACTIVATE or handle the
situation if the PSP firmware returns DFFLUSH_REQUIRED?

[1] https://www.amd.com/system/files/TechDocs/56860.pdf

> +}
> +
> +static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> + struct sev_data_snp_launch_start start = {0};
> + struct kvm_sev_snp_launch_start params;
> + int rc;
> +
> + if (!sev_snp_guest(kvm))
> + return -ENOTTY;
> +
> + if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data, sizeof(params)))
> + return -EFAULT;
> +
> + sev->snp_context = snp_context_create(kvm, argp);
> + if (!sev->snp_context)
> + return -ENOTTY;
> +
> + start.gctx_paddr = __psp_pa(sev->snp_context);
> + start.policy = params.policy;
> + memcpy(start.gosvw, params.gosvw, sizeof(params.gosvw));
> + rc = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_LAUNCH_START, &start, &argp->error);
> + if (rc)
> + goto e_free_context;
> +
> + sev->fd = argp->sev_fd;
> + rc = snp_bind_asid(kvm, &argp->error);
> + if (rc)
> + goto e_free_context;
> +
> + return 0;
> +
> +e_free_context:
> + snp_decommission_context(kvm);
> +
> + return rc;
> +}
> +
> int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
> {
> struct kvm_sev_cmd sev_cmd;
> @@ -2101,6 +2183,9 @@ int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
> case KVM_SEV_RECEIVE_FINISH:
> r = sev_receive_finish(kvm, &sev_cmd);
> break;
> + case KVM_SEV_SNP_LAUNCH_START:
> + r = snp_launch_start(kvm, &sev_cmd);
> + break;
> default:
> r = -EINVAL;
> goto out;
> @@ -2292,6 +2377,28 @@ int sev_vm_copy_enc_context_from(struct kvm *kvm, unsigned int source_fd)
> return ret;
> }
>
> +static int snp_decommission_context(struct kvm *kvm)
> +{
> + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> + struct sev_data_snp_addr data = {};
> + int ret;
> +
> + /* If context is not created then do nothing */
> + if (!sev->snp_context)
> + return 0;
> +
> + data.gctx_paddr = __sme_pa(sev->snp_context);
> + ret = sev_do_cmd(SEV_CMD_SNP_DECOMMISSION, &data, NULL);
> + if (WARN_ONCE(ret, "failed to release guest context"))
> + return ret;
> +
> + /* free the context page now */
> + snp_free_firmware_page(sev->snp_context);
> + sev->snp_context = NULL;
> +
> + return 0;
> +}
> +
> void sev_vm_destroy(struct kvm *kvm)
> {
> struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> @@ -2333,7 +2440,15 @@ void sev_vm_destroy(struct kvm *kvm)
> }
> }
>
> - sev_unbind_asid(kvm, sev->handle);
> + if (sev_snp_guest(kvm)) {
> + if (snp_decommission_context(kvm)) {
> + WARN_ONCE(1, "Failed to free SNP guest context, leaking asid!\n");
> + return;
> + }
> + } else {
> + sev_unbind_asid(kvm, sev->handle);
> + }
> +
> sev_asid_free(sev);
> }
>
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 56a5c96d8a36..740969b57425 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -92,6 +92,7 @@ struct kvm_sev_info {
> struct misc_cg *misc_cg; /* For misc cgroup accounting */
> atomic_t migration_in_progress;
> u64 snp_init_flags;
> + void *snp_context; /* SNP guest context page */
> };
>
> struct kvm_svm {
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 499cc323f793..cf19799ca5ce 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1919,6 +1919,7 @@ enum sev_cmd_id {
>
> /* SNP specific commands */
> KVM_SEV_SNP_INIT,
> + KVM_SEV_SNP_LAUNCH_START,
>
> KVM_SEV_NR_MAX,
> };
> @@ -2026,6 +2027,15 @@ struct kvm_snp_init {
> __u64 flags;
> };
>
> +struct kvm_sev_snp_launch_start {
> + __u64 policy;
> + __u64 ma_uaddr;
> + __u8 ma_en;
> + __u8 imi_en;
> + __u8 gosvw[16];
> + __u8 pad[6];
> +};
> +
> #define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)
> #define KVM_DEV_ASSIGN_PCI_2_3 (1 << 1)
> #define KVM_DEV_ASSIGN_MASK_INTX (1 << 2)

Next message: Rae Moar: "Re: [PATCH v2 3/3] kunit: fix bug of extra newline characters in debugfs logs"
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In reply to: Michael Roth: "[PATCH RFC v8 34/56] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START command"
Next in thread: Michael Roth: "[PATCH RFC v8 32/56] KVM: SVM: Add initial SEV-SNP support"
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