Re: [PATCH Part1 v5 33/38] x86/sev: Provide support for SNP guest request NAEs

Borislav Petkov
2021-08-27T17:43:39Z

On Fri, Aug 20, 2021 at 10:19:28AM -0500, Brijesh Singh wrote:
> +int snp_issue_guest_request(int type, struct snp_guest_request_data *input, unsigned long *fw_err)
> +{
> + struct ghcb_state state;
> + unsigned long id, flags;
> + struct ghcb *ghcb;
> + int ret;
> +
> + if (!sev_feature_enabled(SEV_SNP))
> + return -ENODEV;
> +
> + local_irq_save(flags);
> +
> + ghcb = __sev_get_ghcb(&state);
> + if (!ghcb) {
> + ret = -EIO;
> + goto e_restore_irq;
> + }
> +
> + vc_ghcb_invalidate(ghcb);
> +
> + if (type == GUEST_REQUEST) {
> + id = SVM_VMGEXIT_GUEST_REQUEST;
> + } else if (type == EXT_GUEST_REQUEST) {
> + id = SVM_VMGEXIT_EXT_GUEST_REQUEST;
> + ghcb_set_rax(ghcb, input->data_gpa);
> + ghcb_set_rbx(ghcb, input->data_npages);

Hmmm, now I'm not sure. We did enum psc_op where you simply pass in the
op directly to the hardware because the enum uses the same numbers as
the actual command.

But here that @type thing is simply used to translate to the SVM_VMGEXIT
thing. So maybe you don't need it here and you can hand in the exit_code
directly:

int snp_issue_guest_request(u64 exit_code, struct snp_guest_request_data *input,
unsigned long *fw_err)

which you then pass in directly to...

> + } else {
> + ret = -EINVAL;
> + goto e_put;
> + }
> +
> + ret = sev_es_ghcb_hv_call(ghcb, NULL, id, input->req_gpa, input->resp_gpa);

... this guy here:

ret = sev_es_ghcb_hv_call(ghcb, NULL, exit_code, input->req_gpa, input->resp_gpa);

> + if (ret)
> + goto e_put;
> +
> + if (ghcb->save.sw_exit_info_2) {
> + /* Number of expected pages are returned in RBX */
> + if (id == EXT_GUEST_REQUEST &&
> + ghcb->save.sw_exit_info_2 == SNP_GUEST_REQ_INVALID_LEN)
> + input->data_npages = ghcb_get_rbx(ghcb);
> +
> + if (fw_err)
> + *fw_err = ghcb->save.sw_exit_info_2;
> +
> + ret = -EIO;
> + }
> +
> +e_put:
> + __sev_put_ghcb(&state);
> +e_restore_irq:
> + local_irq_restore(flags);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(snp_issue_guest_request);
> diff --git a/include/linux/sev-guest.h b/include/linux/sev-guest.h

Why is this a separate header in the include/linux/ namespace?

Is SNP available on something which is !x86, all of a sudden?

> new file mode 100644
> index 000000000000..24dd17507789
> --- /dev/null
> +++ b/include/linux/sev-guest.h
> @@ -0,0 +1,48 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * AMD Secure Encrypted Virtualization (SEV) guest driver interface
> + *
> + * Copyright (C) 2021 Advanced Micro Devices, Inc.
> + *
> + * Author: Brijesh Singh <brijesh.singh@amd.com>
> + *
> + */
> +
> +#ifndef __LINUX_SEV_GUEST_H_
> +#define __LINUX_SEV_GUEST_H_
> +
> +#include <linux/types.h>
> +
> +enum vmgexit_type {
> + GUEST_REQUEST,
> + EXT_GUEST_REQUEST,
> +
> + GUEST_REQUEST_MAX
> +};
> +
> +/*
> + * The error code when the data_npages is too small. The error code
> + * is defined in the GHCB specification.
> + */
> +#define SNP_GUEST_REQ_INVALID_LEN 0x100000000ULL

so basically

BIT_ULL(32)

> +
> +struct snp_guest_request_data {

"snp_req_data" I guess is shorter. And having "guest" in there is
probably not needed because snp is always guest-related anyway.

> + unsigned long req_gpa;
> + unsigned long resp_gpa;
> + unsigned long data_gpa;
> + unsigned int data_npages;
> +};
> +
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +int snp_issue_guest_request(int vmgexit_type, struct snp_guest_request_data *input,
> + unsigned long *fw_err);
> +#else
> +
> +static inline int snp_issue_guest_request(int type, struct snp_guest_request_data *input,
> + unsigned long *fw_err)
> +{
> + return -ENODEV;
> +}
> +
> +#endif /* CONFIG_AMD_MEM_ENCRYPT */
> +#endif /* __LINUX_SEV_GUEST_H__ */
> --
> 2.17.1
>

--
Regards/Gruss,
Boris.