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Subject[PATCH v7 34/45] x86/compressed/64: add support for SEV-SNP CPUID table in #VC handlers
Date
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 configurable location in guest memory
that has been pre-populated with a firmware-validated CPUID table to
look up the relevant CPUID values rather than requesting them from
hypervisor via a VMGEXIT. Add the various hooks in the #VC handlers to
allow CPUID instructions to be handled via the table. The code to
actually configure/enable the table will be added in a subsequent
commit.

Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
arch/x86/boot/compressed/sev.c | 1 +
arch/x86/include/asm/sev-common.h | 2 +
arch/x86/kernel/sev-shared.c | 320 ++++++++++++++++++++++++++++++
arch/x86/kernel/sev.c | 1 +
4 files changed, 324 insertions(+)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index fb2f763dfc19..2d9db9dc149b 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -20,6 +20,7 @@
#include <asm/fpu/xcr.h>
#include <asm/ptrace.h>
#include <asm/svm.h>
+#include <asm/cpuid.h>

#include "error.h"

diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index c380aba9fc8d..45c535eb75f1 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -152,6 +152,8 @@ 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/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 9f81d78ab061..b1ed5a1b1a90 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -14,6 +14,41 @@
#define has_cpuflag(f) boot_cpu_has(f)
#endif

+/*
+ * Individual entries of the SEV-SNP CPUID table, as defined by the SEV-SNP
+ * Firmware ABI, Revision 0.9, Section 7.1, Table 14. Note that the XCR0_IN
+ * and XSS_IN are denoted here as __unused/__unused2, since they are not
+ * needed for the current guest implementation, where the size of the buffers
+ * needed to store enabled XSAVE-saved features are calculated rather than
+ * encoded in the CPUID table for each possible combination of XCR0_IN/XSS_IN
+ * to save space.
+ */
+struct snp_cpuid_fn {
+ u32 eax_in;
+ u32 ecx_in;
+ u64 __unused;
+ u64 __unused2;
+ u32 eax;
+ u32 ebx;
+ u32 ecx;
+ u32 edx;
+ u64 __reserved;
+} __packed;
+
+/*
+ * SEV-SNP CPUID table header, as defined by the SEV-SNP Firmware ABI,
+ * Revision 0.9, Section 8.14.2.6. Also noted there is the SEV-SNP
+ * firmware-enforced limit of 64 entries per CPUID table.
+ */
+#define SNP_CPUID_COUNT_MAX 64
+
+struct snp_cpuid_info {
+ u32 count;
+ u32 __reserved1;
+ u64 __reserved2;
+ struct snp_cpuid_fn fn[SNP_CPUID_COUNT_MAX];
+} __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 +61,20 @@ static u16 ghcb_version __ro_after_init;
/* Bitmap of SEV features supported by the hypervisor */
static u64 sev_hv_features __ro_after_init;

+/* Copy of the SNP firmware's CPUID page. */
+static struct snp_cpuid_info cpuid_info_copy __ro_after_init;
+static bool snp_cpuid_initialized __ro_after_init;
+
+/*
+ * These will be initialized based on CPUID table so that non-present
+ * all-zero leaves (for sparse tables) can be differentiated from
+ * invalid/out-of-range leaves. This is needed since all-zero leaves
+ * still need to be post-processed.
+ */
+u32 cpuid_std_range_max __ro_after_init;
+u32 cpuid_hyp_range_max __ro_after_init;
+u32 cpuid_ext_range_max __ro_after_init;
+
static bool __init sev_es_check_cpu_features(void)
{
if (!has_cpuflag(X86_FEATURE_RDRAND)) {
@@ -256,6 +305,244 @@ static int sev_cpuid_hv(u32 func, u32 subfunc, u32 *eax, u32 *ebx,
return 0;
}

+static const struct snp_cpuid_info *
+snp_cpuid_info_get_ptr(void)
+{
+ void *ptr;
+
+ /*
+ * This may be called early while still running on the initial identity
+ * mapping. Use RIP-relative addressing to obtain the correct address
+ * in both for identity mapping and after switch-over to kernel virtual
+ * addresses.
+ */
+ asm ("lea cpuid_info_copy(%%rip), %0"
+ : "=r" (ptr)
+ : "p" (&cpuid_info_copy));
+
+ return ptr;
+}
+
+static inline bool snp_cpuid_active(void)
+{
+ return snp_cpuid_initialized;
+}
+
+static int snp_cpuid_calc_xsave_size(u64 xfeatures_en, u32 base_size,
+ u32 *xsave_size, bool compacted)
+{
+ const struct snp_cpuid_info *cpuid_info = snp_cpuid_info_get_ptr();
+ u32 xsave_size_total = base_size;
+ u64 xfeatures_found = 0;
+ int i;
+
+ for (i = 0; i < cpuid_info->count; i++) {
+ const struct 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 & (BIT_ULL(fn->ecx_in))))
+ continue;
+ if (xfeatures_found & (BIT_ULL(fn->ecx_in)))
+ continue;
+
+ xfeatures_found |= (BIT_ULL(fn->ecx_in));
+
+ if (compacted)
+ xsave_size_total += fn->eax;
+ else
+ xsave_size_total = max(xsave_size_total,
+ fn->eax + fn->ebx);
+ }
+
+ /*
+ * 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 & GENMASK_ULL(63, 2)))
+ return -EINVAL;
+
+ *xsave_size = xsave_size_total;
+
+ return 0;
+}
+
+static void snp_cpuid_hv(u32 func, u32 subfunc, u32 *eax, u32 *ebx, u32 *ecx,
+ u32 *edx)
+{
+ /*
+ * MSR protocol does not support fetching indexed subfunction, but is
+ * sufficient to handle current fallback cases. Should that change,
+ * make sure to terminate rather than ignoring the index and grabbing
+ * random values. If this issue arises in the future, handling can be
+ * added here to use GHCB-page protocol for cases that occur late
+ * enough in boot that GHCB page is available.
+ */
+ if (cpuid_function_is_indexed(func) && subfunc)
+ 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
+snp_cpuid_find_validated_func(u32 func, u32 subfunc, u32 *eax, u32 *ebx,
+ u32 *ecx, u32 *edx)
+{
+ const struct snp_cpuid_info *cpuid_info = snp_cpuid_info_get_ptr();
+ int i;
+
+ for (i = 0; i < cpuid_info->count; i++) {
+ const struct 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;
+
+ return true;
+ }
+
+ return false;
+}
+
+static bool snp_cpuid_check_range(u32 func)
+{
+ if (func <= cpuid_std_range_max ||
+ (func >= 0x40000000 && func <= cpuid_hyp_range_max) ||
+ (func >= 0x80000000 && func <= cpuid_ext_range_max))
+ return true;
+
+ return false;
+}
+
+static int snp_cpuid_postprocess(u32 func, u32 subfunc, u32 *eax, u32 *ebx,
+ u32 *ecx, u32 *edx)
+{
+ u32 ebx2, ecx2, edx2;
+
+ switch (func) {
+ case 0x1:
+ snp_cpuid_hv(func, subfunc, NULL, &ebx2, NULL, &edx2);
+
+ /* initial APIC ID */
+ *ebx = (ebx2 & GENMASK(31, 24)) | (*ebx & GENMASK(23, 0));
+ /* APIC enabled bit */
+ *edx = (edx2 & BIT(9)) | (*edx & ~BIT(9));
+
+ /* OSXSAVE enabled bit */
+ if (native_read_cr4() & X86_CR4_OSXSAVE)
+ *ecx |= BIT(27);
+ break;
+ case 0x7:
+ /* OSPKE enabled bit */
+ *ecx &= ~BIT(4);
+ if (native_read_cr4() & X86_CR4_PKE)
+ *ecx |= BIT(4);
+ break;
+ case 0xB:
+ /* extended APIC ID */
+ snp_cpuid_hv(func, 0, NULL, NULL, NULL, edx);
+ break;
+ case 0xD: {
+ bool compacted = false;
+ u64 xcr0 = 1, xss = 0;
+ u32 xsave_size;
+
+ if (subfunc != 0 && subfunc != 1)
+ return 0;
+
+ if (native_read_cr4() & X86_CR4_OSXSAVE)
+ xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
+ if (subfunc == 1) {
+ /* Get XSS value if XSAVES is enabled. */
+ if (*eax & BIT(3)) {
+ unsigned long lo, hi;
+
+ asm volatile("rdmsr" : "=a" (lo), "=d" (hi)
+ : "c" (MSR_IA32_XSS));
+ xss = (hi << 32) | lo;
+ }
+
+ /*
+ * 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 (feature bit 1) or XSAVES (feature
+ * bit 3) since SNP-capable hardware has these feature
+ * bits 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 for SEV-SNP guests.
+ */
+ if (!(*eax & (BIT(1) | BIT(3))))
+ return -EINVAL;
+
+ compacted = true;
+ }
+
+ if (snp_cpuid_calc_xsave_size(xcr0 | xss, *ebx, &xsave_size,
+ compacted))
+ return -EINVAL;
+
+ *ebx = xsave_size;
+ }
+ break;
+ case 0x8000001E:
+ /* extended APIC ID */
+ snp_cpuid_hv(func, subfunc, eax, &ebx2, &ecx2, NULL);
+ /* compute ID */
+ *ebx = (*ebx & GENMASK(31, 8)) | (ebx2 & GENMASK(7, 0));
+ /* node ID */
+ *ecx = (*ecx & GENMASK(31, 8)) | (ecx2 & GENMASK(7, 0));
+ break;
+ default:
+ /* No fix-ups needed, use values as-is. */
+ break;
+ }
+
+ return 0;
+}
+
+/*
+ * Returns -EOPNOTSUPP if feature not enabled. Any other return value should be
+ * treated as fatal by caller.
+ */
+static int snp_cpuid(u32 func, u32 subfunc, u32 *eax, u32 *ebx, u32 *ecx,
+ u32 *edx)
+{
+ if (!snp_cpuid_active())
+ return -EOPNOTSUPP;
+
+ if (!snp_cpuid_find_validated_func(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). This is useful here
+ * as well as it allows virtually all guest configurations to
+ * work using a single SEV-SNP CPUID table.
+ *
+ * To allow for this, there is a need 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 during post-processing. So if it's
+ * not in the table, but is still in the valid range, proceed
+ * with the post-processing. Otherwise, just return zeros.
+ */
+ *eax = *ebx = *ecx = *edx = 0;
+ if (!snp_cpuid_check_range(func))
+ return 0;
+ }
+
+ return snp_cpuid_postprocess(func, subfunc, eax, ebx, ecx, edx);
+}
+
/*
* 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
@@ -263,16 +550,26 @@ 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 subfn = lower_bits(regs->cx, 32);
unsigned int fn = lower_bits(regs->ax, 32);
u32 eax, ebx, ecx, edx;
+ int ret;

/* Only CPUID is supported via MSR protocol */
if (exit_code != SVM_EXIT_CPUID)
goto fail;

+ ret = snp_cpuid(fn, subfn, &eax, &ebx, &ecx, &edx);
+ if (ret == 0)
+ goto cpuid_done;
+
+ if (ret != -EOPNOTSUPP)
+ goto fail;
+
if (sev_cpuid_hv(fn, 0, &eax, &ebx, &ecx, &edx))
goto fail;

+cpuid_done:
regs->ax = eax;
regs->bx = ebx;
regs->cx = ecx;
@@ -567,12 +864,35 @@ static enum es_result vc_handle_ioio(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
return ret;
}

+static int vc_handle_cpuid_snp(struct pt_regs *regs)
+{
+ u32 eax, ebx, ecx, edx;
+ int ret;
+
+ ret = snp_cpuid(regs->ax, regs->cx, &eax, &ebx, &ecx, &edx);
+ if (ret == 0) {
+ regs->ax = eax;
+ regs->bx = ebx;
+ regs->cx = ecx;
+ regs->dx = edx;
+ }
+
+ return ret;
+}
+
static enum es_result vc_handle_cpuid(struct ghcb *ghcb,
struct es_em_ctxt *ctxt)
{
struct pt_regs *regs = ctxt->regs;
u32 cr4 = native_read_cr4();
enum es_result ret;
+ int snp_cpuid_ret;
+
+ snp_cpuid_ret = vc_handle_cpuid_snp(regs);
+ if (snp_cpuid_ret == 0)
+ return ES_OK;
+ if (snp_cpuid_ret != -EOPNOTSUPP)
+ return ES_VMM_ERROR;

ghcb_set_rax(ghcb, regs->ax);
ghcb_set_rcx(ghcb, regs->cx);
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index e966b93212c7..403ae5cddbe8 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -33,6 +33,7 @@
#include <asm/smp.h>
#include <asm/cpu.h>
#include <asm/apic.h>
+#include <asm/cpuid.h>

#define DR7_RESET_VALUE 0x400

--
2.25.1
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