Re: [PATCH Part1 v5 28/38] x86/compressed/64: enable SEV-SNP-validated CPUID in #VC handler

Borislav Petkov
2021-08-25T19:18:50Z

On Fri, Aug 20, 2021 at 10:19:23AM -0500, Brijesh Singh wrote:
> From: Michael Roth <michael.roth@amd.com>
>
> CPUID instructions generate a #VC exception for SEV-ES/SEV-SNP guests,
> for which early handlers are currently set up to handle. In the case
> of SEV-SNP, guests can use a special location in guest memory address
> space that has been pre-populated with firmware-validated CPUID
> information to look up the relevant CPUID values rather than
> requesting them from hypervisor via a VMGEXIT.
>
> Determine the location of the CPUID memory address in advance of any
> CPUID instructions/exceptions and, when available, use it to handle
> the CPUID lookup.
>
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> arch/x86/boot/compressed/efi.c | 1 +
> arch/x86/boot/compressed/head_64.S | 1 +
> arch/x86/boot/compressed/idt_64.c | 7 +-
> arch/x86/boot/compressed/misc.h | 1 +
> arch/x86/boot/compressed/sev.c | 3 +
> arch/x86/include/asm/sev-common.h | 2 +
> arch/x86/include/asm/sev.h | 3 +
> arch/x86/kernel/sev-shared.c | 374 +++++++++++++++++++++++++++++
> arch/x86/kernel/sev.c | 4 +
> 9 files changed, 394 insertions(+), 2 deletions(-)

Another huuge patch. I wonder if it can be split...

> diff --git a/arch/x86/boot/compressed/efi.c b/arch/x86/boot/compressed/efi.c
> index 16ff5cb9a1fb..a1529a230ea7 100644
> --- a/arch/x86/boot/compressed/efi.c
> +++ b/arch/x86/boot/compressed/efi.c
> @@ -176,3 +176,4 @@ efi_get_conf_table(struct boot_params *boot_params,
>
> return 0;
> }
> +

Applying: x86/compressed/64: Enable SEV-SNP-validated CPUID in #VC handler
.git/rebase-apply/patch:21: new blank line at EOF.
+
warning: 1 line adds whitespace errors.

That looks like a stray hunk which doesn't belong.

> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> index a2347ded77ea..1c1658693fc9 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -441,6 +441,7 @@ SYM_CODE_START(startup_64)
> .Lon_kernel_cs:
>
> pushq %rsi
> + movq %rsi, %rdi /* real mode address */
> call load_stage1_idt
> popq %rsi
>
> diff --git a/arch/x86/boot/compressed/idt_64.c b/arch/x86/boot/compressed/idt_64.c
> index 9b93567d663a..1f6511a6625d 100644
> --- a/arch/x86/boot/compressed/idt_64.c
> +++ b/arch/x86/boot/compressed/idt_64.c
> @@ -3,6 +3,7 @@
> #include <asm/segment.h>
> #include <asm/trapnr.h>
> #include "misc.h"
> +#include <asm/sev.h>

asm/ namespaced headers should go together, before the private ones,
i.e., above the misc.h line.

> static void set_idt_entry(int vector, void (*handler)(void))
> {
> @@ -28,13 +29,15 @@ static void load_boot_idt(const struct desc_ptr *dtr)
> }
>
> /* Setup IDT before kernel jumping to .Lrelocated */
> -void load_stage1_idt(void)
> +void load_stage1_idt(void *rmode)
> {
> boot_idt_desc.address = (unsigned long)boot_idt;
>
>
> - if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
> + if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
> + sev_snp_cpuid_init(rmode);
> set_idt_entry(X86_TRAP_VC, boot_stage1_vc);
> + }
>
> load_boot_idt(&boot_idt_desc);
> }
> diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
> index 16b092fd7aa1..cdd328aa42c2 100644
> --- a/arch/x86/boot/compressed/misc.h
> +++ b/arch/x86/boot/compressed/misc.h
> @@ -190,6 +190,7 @@ int efi_get_conf_table(struct boot_params *boot_params,
> unsigned long *conf_table_pa,
> unsigned int *conf_table_len,
> bool *is_efi_64);
> +

Another stray hunk.

> #else
> static inline int
> efi_find_vendor_table(unsigned long conf_table_pa, unsigned int conf_table_len,
> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> index 6e8d97c280aa..910bf5cf010e 100644
> --- a/arch/x86/boot/compressed/sev.c
> +++ b/arch/x86/boot/compressed/sev.c
> @@ -20,6 +20,9 @@
> #include <asm/fpu/xcr.h>
> #include <asm/ptrace.h>
> #include <asm/svm.h>
> +#include <asm/cpuid.h>
> +#include <linux/efi.h>
> +#include <linux/log2.h>

What are those includes for?

Polluting the decompressor namespace with kernel proper defines is a
real pain to untangle as it is. What do you need those for and can you
do it without them?

> #include "error.h"
>
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index 072540dfb129..5f134c172dbf 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -148,6 +148,8 @@ struct snp_psc_desc {
> #define GHCB_TERM_PSC 1 /* Page State Change failure */
> #define GHCB_TERM_PVALIDATE 2 /* Pvalidate failure */
> #define GHCB_TERM_NOT_VMPL0 3 /* SNP guest is not running at VMPL-0 */
> +#define GHCB_TERM_CPUID 4 /* CPUID-validation failure */
> +#define GHCB_TERM_CPUID_HV 5 /* CPUID failure during hypervisor fallback */
>
> #define GHCB_RESP_CODE(v) ((v) & GHCB_MSR_INFO_MASK)
>
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 534fa1c4c881..c73931548346 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -11,6 +11,7 @@
> #include <linux/types.h>
> #include <asm/insn.h>
> #include <asm/sev-common.h>
> +#include <asm/bootparam.h>
>
> #define GHCB_PROTOCOL_MIN 1ULL
> #define GHCB_PROTOCOL_MAX 2ULL
> @@ -126,6 +127,7 @@ void __init snp_prep_memory(unsigned long paddr, unsigned int sz, enum psc_op op
> void snp_set_memory_shared(unsigned long vaddr, unsigned int npages);
> void snp_set_memory_private(unsigned long vaddr, unsigned int npages);
> void snp_set_wakeup_secondary_cpu(void);
> +void sev_snp_cpuid_init(struct boot_params *bp);
> #else
> static inline void sev_es_ist_enter(struct pt_regs *regs) { }
> static inline void sev_es_ist_exit(void) { }
> @@ -141,6 +143,7 @@ static inline void __init snp_prep_memory(unsigned long paddr, unsigned int sz,
> static inline void snp_set_memory_shared(unsigned long vaddr, unsigned int npages) { }
> static inline void snp_set_memory_private(unsigned long vaddr, unsigned int npages) { }
> static inline void snp_set_wakeup_secondary_cpu(void) { }
> +static inline void sev_snp_cpuid_init(struct boot_params *bp) { }
> #endif
>
> #endif
> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
> index ae4556925485..651980ddbd65 100644
> --- a/arch/x86/kernel/sev-shared.c
> +++ b/arch/x86/kernel/sev-shared.c
> @@ -14,6 +14,25 @@
> #define has_cpuflag(f) boot_cpu_has(f)
> #endif
>
> +struct sev_snp_cpuid_fn {
> + u32 eax_in;
> + u32 ecx_in;
> + u64 unused;
> + u64 unused2;

What are those for? Padding? Or are they spec-ed somewhere and left for
future use?

Seeing how the struct is __packed, they probably are part of a spec
definition somewhere.

Link pls.

> + u32 eax;
> + u32 ebx;
> + u32 ecx;
> + u32 edx;
> + u64 reserved;

Ditto.

Please prefix all those unused/reserved members with "__".

> +} __packed;
> +
> +struct sev_snp_cpuid_info {
> + u32 count;
> + u32 reserved1;
> + u64 reserved2;

Ditto.

> + struct sev_snp_cpuid_fn fn[0];
> +} __packed;
> +
> /*
> * Since feature negotiation related variables are set early in the boot
> * process they must reside in the .data section so as not to be zeroed
> @@ -26,6 +45,15 @@ static u16 __ro_after_init ghcb_version;
> /* Bitmap of SEV features supported by the hypervisor */
> u64 __ro_after_init sev_hv_features = 0;
>
> +/*
> + * These are also stored in .data section to avoid the need to re-parse
> + * boot_params and re-determine CPUID memory range when .bss is cleared.
> + */
> +static int sev_snp_cpuid_enabled __section(".data");

That will become part of prot_guest_has() or cc_platform_has() or
whatever its name is going to be.

> +static unsigned long sev_snp_cpuid_pa __section(".data");
> +static unsigned long sev_snp_cpuid_sz __section(".data");
> +static const struct sev_snp_cpuid_info *cpuid_info __section(".data");

All those: __ro_after_init?

Also, just like the ones above have a short comment explaining what they
are, add such comments for those too pls and perhaps what they're used
for.

> +
> static bool __init sev_es_check_cpu_features(void)
> {
> if (!has_cpuflag(X86_FEATURE_RDRAND)) {
> @@ -236,6 +264,219 @@ static int sev_cpuid_hv(u32 func, u32 subfunc, u32 *eax, u32 *ebx,
> return 0;
> }
>
> +static bool sev_snp_cpuid_active(void)
> +{
> + return sev_snp_cpuid_enabled;
> +}

That too will become part of prot_guest_has() or cc_platform_has() or
whatever its name is going to be.

> +
> +static int sev_snp_cpuid_xsave_size(u64 xfeatures_en, u32 base_size,
> + u32 *xsave_size, bool compacted)

Function name needs a verb. Please audit all your patches.

> +{
> + u64 xfeatures_found = 0;
> + int i;
> +
> + *xsave_size = base_size;

Set that xsave_size only...
> +
> + for (i = 0; i < cpuid_info->count; i++) {
> + const struct sev_snp_cpuid_fn *fn = &cpuid_info->fn[i];
> +
> + if (!(fn->eax_in == 0xd && fn->ecx_in > 1 && fn->ecx_in < 64))
> + continue;
> + if (!(xfeatures_en & (1UL << fn->ecx_in)))
> + continue;
> + if (xfeatures_found & (1UL << fn->ecx_in))
> + continue;
> +
> + xfeatures_found |= (1UL << fn->ecx_in);

For all use BIT_ULL().

> + if (compacted)
> + *xsave_size += fn->eax;
> + else
> + *xsave_size = max(*xsave_size, fn->eax + fn->ebx);

... not here ...

> + }
> +
> + /*
> + * Either the guest set unsupported XCR0/XSS bits, or the corresponding
> + * entries in the CPUID table were not present. This is not a valid
> + * state to be in.
> + */
> + if (xfeatures_found != (xfeatures_en & ~3ULL))
> + return -EINVAL;

... but here when you're not going to return an error because callers
will see that value change temporarily which is not clean.

Also, you need to set it once - not during each loop iteration.

> +
> + return 0;
> +}
> +
> +static void sev_snp_cpuid_hv(u32 func, u32 subfunc, u32 *eax, u32 *ebx,
> + u32 *ecx, u32 *edx)
> +{
> + /*
> + * Currently MSR protocol is sufficient to handle fallback cases, but
> + * should that change make sure we terminate rather than grabbing random

Fix the "we"s please. Please audit all your patches.

> + * values. Handling can be added in future to use GHCB-page protocol for
> + * cases that occur late enough in boot that GHCB page is available

End comment sentences with a fullstop. Please audit all your patches.

> + */

Also, put that comment over the function.

> + if (cpuid_function_is_indexed(func) && subfunc != 0)

In all your patches:

s/ != 0//g

> + sev_es_terminate(1, GHCB_TERM_CPUID_HV);
> +
> + if (sev_cpuid_hv(func, 0, eax, ebx, ecx, edx))
> + sev_es_terminate(1, GHCB_TERM_CPUID_HV);
> +}
> +
> +static bool sev_snp_cpuid_find(u32 func, u32 subfunc, u32 *eax, u32 *ebx,

I guess

find_validated_cpuid_func()

or so to denote where it picks it out from.

> + u32 *ecx, u32 *edx)
> +{
> + int i;
> + bool found = false;

The tip-tree preferred ordering of variable declarations at the
beginning of a function is reverse fir tree order::

struct long_struct_name *descriptive_name;
unsigned long foo, bar;
unsigned int tmp;
int ret;

The above is faster to parse than the reverse ordering::

int ret;
unsigned int tmp;
unsigned long foo, bar;
struct long_struct_name *descriptive_name;

And even more so than random ordering::

unsigned long foo, bar;
int ret;
struct long_struct_name *descriptive_name;
unsigned int tmp;

Audit all your patches pls.

> +
> + for (i = 0; i < cpuid_info->count; i++) {
> + const struct sev_snp_cpuid_fn *fn = &cpuid_info->fn[i];
> +
> + if (fn->eax_in != func)
> + continue;
> +
> + if (cpuid_function_is_indexed(func) && fn->ecx_in != subfunc)
> + continue;
> +
> + *eax = fn->eax;
> + *ebx = fn->ebx;
> + *ecx = fn->ecx;
> + *edx = fn->edx;
> + found = true;
> +
> + break;

That's just silly. Simply:

return true;

> + }
> +
> + return found;

return false;

here and the "found" variable can go.

> +}
> +
> +static bool sev_snp_cpuid_in_range(u32 func)
> +{
> + int i;
> + u32 std_range_min = 0;
> + u32 std_range_max = 0;
> + u32 hyp_range_min = 0x40000000;
> + u32 hyp_range_max = 0;
> + u32 ext_range_min = 0x80000000;
> + u32 ext_range_max = 0;
> +
> + for (i = 0; i < cpuid_info->count; i++) {
> + const struct sev_snp_cpuid_fn *fn = &cpuid_info->fn[i];
> +
> + if (fn->eax_in == std_range_min)
> + std_range_max = fn->eax;
> + else if (fn->eax_in == hyp_range_min)
> + hyp_range_max = fn->eax;
> + else if (fn->eax_in == ext_range_min)
> + ext_range_max = fn->eax;
> + }

So this loop which determines those ranges will run each time
sev_snp_cpuid_find() doesn't find @func among the validated CPUID leafs.

Why don't you do that determination once at init...

> +
> + if ((func >= std_range_min && func <= std_range_max) ||
> + (func >= hyp_range_min && func <= hyp_range_max) ||
> + (func >= ext_range_min && func <= ext_range_max))

... so that this function becomes only this check?

This is unnecessary work as it is.

> + return true;
> +
> + return false;
> +}
> +
> +/*
> + * Returns -EOPNOTSUPP if feature not enabled. Any other return value should be
> + * treated as fatal by caller since we cannot fall back to hypervisor to fetch
> + * the values for security reasons (outside of the specific cases handled here)
> + */
> +static int sev_snp_cpuid(u32 func, u32 subfunc, u32 *eax, u32 *ebx, u32 *ecx,
> + u32 *edx)
> +{
> + if (!sev_snp_cpuid_active())
> + return -EOPNOTSUPP;
> +
> + if (!cpuid_info)
> + return -EIO;
> +
> + if (!sev_snp_cpuid_find(func, subfunc, eax, ebx, ecx, edx)) {
> + /*
> + * Some hypervisors will avoid keeping track of CPUID entries
> + * where all values are zero, since they can be handled the
> + * same as out-of-range values (all-zero). In our case, we want
> + * to be able to distinguish between out-of-range entries and
> + * in-range zero entries, since the CPUID table entries are
> + * only a template that may need to be augmented with
> + * additional values for things like CPU-specific information.
> + * So if it's not in the table, but is still in the valid
> + * range, proceed with the fix-ups below. Otherwise, just return
> + * zeros.
> + */
> + *eax = *ebx = *ecx = *edx = 0;
> + if (!sev_snp_cpuid_in_range(func))
> + goto out;

That label is not needed.

> + }

All that from here on looks like it should go into a separate function
called

snp_cpuid_postprocess()

where you can do a switch-case on func and have it nice, readable and
extensible there, in case more functions get added.

> + if (func == 0x1) {
> + u32 ebx2, edx2;
> +
> + sev_snp_cpuid_hv(func, subfunc, NULL, &ebx2, NULL, &edx2);
> + /* initial APIC ID */
> + *ebx = (*ebx & 0x00FFFFFF) | (ebx2 & 0xFF000000);

For all hex masks: use GENMASK_ULL.

> + /* APIC enabled bit */
> + *edx = (*edx & ~BIT_ULL(9)) | (edx2 & BIT_ULL(9));
> +
> + /* OSXSAVE enabled bit */
> + if (native_read_cr4() & X86_CR4_OSXSAVE)
> + *ecx |= BIT_ULL(27);
> + } else if (func == 0x7) {
> + /* OSPKE enabled bit */
> + *ecx &= ~BIT_ULL(4);
> + if (native_read_cr4() & X86_CR4_PKE)
> + *ecx |= BIT_ULL(4);
> + } else if (func == 0xB) {
> + /* extended APIC ID */
> + sev_snp_cpuid_hv(func, 0, NULL, NULL, NULL, edx);
> + } else if (func == 0xd && (subfunc == 0x0 || subfunc == 0x1)) {
> + bool compacted = false;
> + u64 xcr0 = 1, xss = 0;
> + u32 xsave_size;
> +
> + if (native_read_cr4() & X86_CR4_OSXSAVE)
> + xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
> + if (subfunc == 1) {
> + /* boot/compressed doesn't set XSS so 0 is fine there */
> +#ifndef __BOOT_COMPRESSED
> + if (*eax & 0x8) /* XSAVES */
> + if (boot_cpu_has(X86_FEATURE_XSAVES))

cpu_feature_enabled()

> + rdmsrl(MSR_IA32_XSS, xss);
> +#endif
> + /*
> + * The PPR and APM aren't clear on what size should be
> + * encoded in 0xD:0x1:EBX when compaction is not enabled
> + * by either XSAVEC or XSAVES since SNP-capable hardware
> + * has the entries fixed as 1. KVM sets it to 0 in this
> + * case, but to avoid this becoming an issue it's safer
> + * to simply treat this as unsupported or SNP guests.
> + */
> + if (!(*eax & 0xA)) /* (XSAVEC|XSAVES) */

Please put side comments over the line they comment.

> + return -EINVAL;
> +
> + compacted = true;
> + }
> +
> + if (sev_snp_cpuid_xsave_size(xcr0 | xss, *ebx, &xsave_size,
> + compacted))

No need for that linebreak.

> + return -EINVAL;
> +
> + *ebx = xsave_size;
> + } else if (func == 0x8000001E) {
> + u32 ebx2, ecx2;
> +
> + /* extended APIC ID */
> + sev_snp_cpuid_hv(func, subfunc, eax, &ebx2, &ecx2, NULL);
> + /* compute ID */
> + *ebx = (*ebx & 0xFFFFFFF00) | (ebx2 & 0x000000FF);
> + /* node ID */
> + *ecx = (*ecx & 0xFFFFFFF00) | (ecx2 & 0x000000FF);
> + }
> +
> +out:
> + return 0;
> +}
> +
> /*
> * Boot VC Handler - This is the first VC handler during boot, there is no GHCB
> * page yet, so it only supports the MSR based communication with the

Is that comment...

> @@ -244,15 +485,25 @@ static int sev_cpuid_hv(u32 func, u32 subfunc, u32 *eax, u32 *ebx,
> void __init do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code)
> {
> unsigned int fn = lower_bits(regs->ax, 32);
> + unsigned int subfn = lower_bits(regs->cx, 32);
> u32 eax, ebx, ecx, edx;
> + int ret;
>
> /* Only CPUID is supported via MSR protocol */

... and that still valid?

> if (exit_code != SVM_EXIT_CPUID)
> goto fail;
>
> + ret = sev_snp_cpuid(fn, subfn, &eax, &ebx, &ecx, &edx);
> + if (ret == 0)
> + goto out;

I think you mean here "goto cpuid_done;" or so.

> +
> + if (ret != -EOPNOTSUPP)
> + goto fail;
> +
> if (sev_cpuid_hv(fn, 0, &eax, &ebx, &ecx, &edx))
> goto fail;
>
> +out:
> regs->ax = eax;
> regs->bx = ebx;
> regs->cx = ecx;
> @@ -552,6 +803,19 @@ static enum es_result vc_handle_cpuid(struct ghcb *ghcb,
> struct pt_regs *regs = ctxt->regs;
> u32 cr4 = native_read_cr4();
> enum es_result ret;
> + u32 eax, ebx, ecx, edx;
> + int cpuid_ret;
> +
> + cpuid_ret = sev_snp_cpuid(regs->ax, regs->cx, &eax, &ebx, &ecx, &edx);
> + if (cpuid_ret == 0) {
> + regs->ax = eax;
> + regs->bx = ebx;
> + regs->cx = ecx;
> + regs->dx = edx;
> + return ES_OK;
> + }
> + if (cpuid_ret != -EOPNOTSUPP)
> + return ES_VMM_ERROR;

I don't like this thing slapped inside the function. Pls put it in a separate

vc_handle_cpuid_snp()

which is called by vc_handle_cpuid() instead.

>
> ghcb_set_rax(ghcb, regs->ax);
> ghcb_set_rcx(ghcb, regs->cx);
> @@ -603,3 +867,113 @@ static enum es_result vc_handle_rdtsc(struct ghcb *ghcb,
>
> return ES_OK;
> }
> +
> +#ifdef BOOT_COMPRESSED
> +static struct setup_data *get_cc_setup_data(struct boot_params *bp)
> +{
> + struct setup_data *hdr = (struct setup_data *)bp->hdr.setup_data;
> +
> + while (hdr) {
> + if (hdr->type == SETUP_CC_BLOB)
> + return hdr;
> + hdr = (struct setup_data *)hdr->next;
> + }
> +
> + return NULL;
> +}
> +
> +/*
> + * For boot/compressed kernel:
> + *
> + * 1) Search for CC blob in the following order/precedence:
> + * - via linux boot protocol / setup_data entry
> + * - via EFI configuration table
> + * 2) Return a pointer to the CC blob, NULL otherwise.
> + */
> +static struct cc_blob_sev_info *sev_snp_probe_cc_blob(struct boot_params *bp)

snp_find_cc_blob() simply.

> +{
> + struct cc_blob_sev_info *cc_info = NULL;
> + struct setup_data_cc {
> + struct setup_data header;
> + u32 cc_blob_address;
> + } *sd;

Define that struct above the function and call it "cc_setup_data" like
the rest of the stuff which deals with that.

> + unsigned long conf_table_pa;
> + unsigned int conf_table_len;
> + bool efi_64;
> +
> + /* Try to get CC blob via setup_data */
> + sd = (struct setup_data_cc *)get_cc_setup_data(bp);
> + if (sd) {
> + cc_info = (struct cc_blob_sev_info *)(unsigned long)sd->cc_blob_address;
> + goto out_verify;
> + }
> +
> + /* CC blob isn't in setup_data, see if it's in the EFI config table */
> + if (!efi_get_conf_table(bp, &conf_table_pa, &conf_table_len, &efi_64))
> + (void)efi_find_vendor_table(conf_table_pa, conf_table_len,
> + EFI_CC_BLOB_GUID, efi_64,
> + (unsigned long *)&cc_info);

Yah, check that retval pls with a proper ret variable. No need to cram
it all together.

> +
> +out_verify:
> + /* CC blob should be either valid or not present. Fail otherwise. */
> + if (cc_info && cc_info->magic != CC_BLOB_SEV_HDR_MAGIC)
> + sev_es_terminate(1, GHCB_SNP_UNSUPPORTED);
> +
> + return cc_info;
> +}
> +#else
> +/*
> + * Probing for CC blob for run-time kernel will be enabled in a subsequent
> + * patch. For now we need to stub this out.
> + */
> +static struct cc_blob_sev_info *sev_snp_probe_cc_blob(struct boot_params *bp)
> +{
> + return NULL;
> +}
> +#endif
> +
> +/*
> + * Initial set up of CPUID table when running identity-mapped.
> + *
> + * NOTE: Since SEV_SNP feature partly relies on CPUID checks that can't
> + * happen until we access CPUID page, we skip the check and hope the
> + * bootloader is providing sane values.

So I don't like the sound of that even one bit. We shouldn't hope
anything here...

> Current code relies on all CPUID
> + * page lookups originating from #VC handler, which at least provides
> + * indication that SEV-ES is enabled. Subsequent init levels will check for
> + * SEV_SNP feature once available to also take SEV MSR value into account.
> + */
> +void sev_snp_cpuid_init(struct boot_params *bp)

snp_cpuid_init()

In general, prefix all SNP-specific variables, structs, functions, etc
with "snp_" simply.

> +{
> + struct cc_blob_sev_info *cc_info;
> +
> + if (!bp)
> + sev_es_terminate(1, GHCB_TERM_CPUID);
> +
> + cc_info = sev_snp_probe_cc_blob(bp);
> +

^ Superfluous newline.

> + if (!cc_info)
> + return;
> +
> + sev_snp_cpuid_pa = cc_info->cpuid_phys;
> + sev_snp_cpuid_sz = cc_info->cpuid_len;

You can do those assignments ...

> +
> + /*
> + * These should always be valid values for SNP, even if guest isn't
> + * actually configured to use the CPUID table.
> + */
> + if (!sev_snp_cpuid_pa || sev_snp_cpuid_sz < PAGE_SIZE)
> + sev_es_terminate(1, GHCB_TERM_CPUID);

... here, after you've verified them.

> +
> + cpuid_info = (const struct sev_snp_cpuid_info *)sev_snp_cpuid_pa;
> +
> + /*
> + * We should be able to trust the 'count' value in the CPUID table
> + * area, but ensure it agrees with CC blob value to be safe.
> + */
> + if (sev_snp_cpuid_sz < (sizeof(struct sev_snp_cpuid_info) +
> + sizeof(struct sev_snp_cpuid_fn) *
> + cpuid_info->count))

Yah, this is the type of paranoia I'm talking about!

> + sev_es_terminate(1, GHCB_TERM_CPUID);
> +
> + sev_snp_cpuid_enabled = 1;
> +}
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index ddf8ced4a879..d7b6f7420551 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -19,6 +19,8 @@
> #include <linux/kernel.h>
> #include <linux/mm.h>
> #include <linux/cpumask.h>
> +#include <linux/log2.h>
> +#include <linux/efi.h>
>
> #include <asm/cpu_entry_area.h>
> #include <asm/stacktrace.h>
> @@ -32,6 +34,8 @@
> #include <asm/smp.h>
> #include <asm/cpu.h>
> #include <asm/apic.h>
> +#include <asm/efi.h>
> +#include <asm/cpuid.h>
>
> #include "sev-internal.h"

What are those includes for?

Looks like a leftover...

--
Regards/Gruss,
Boris.