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

Brijesh Singh
2021-08-27T18:08:08Z

On 8/27/21 12:44 PM, Borislav Petkov wrote:
> 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...

Okay, works for me. The main reason why I choose the enum was to not
expose the GHCB exit code to the driver but I guess that attestation
driver need to know which VMGEXIT need to be called, so, its okay to
have it pass the VMGEXIT number instead of enum.

>> + } 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?

So far most of the changes were in x86 specific files. However, the
attestation service is available through a driver to the userspace. The
driver needs to use the VMGEXIT routines provides by the x86 core. I
created the said header file so that driver does not need to include
<asm/sev.h/sev-common.h> etc and will compile for !x86.

>> 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)

Noted.

>
>> +
>> +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.

Noted.

>> + 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
>>