[PATCH v12 31/46] x86/sev: Move MSR-based VMGEXITs for CPUID to helper

Brijesh Singh
2022-03-07T21:38:57Z

From: Michael Roth <michael.roth@amd.com>

This code will also be used later for SEV-SNP-validated CPUID code in
some cases, so move it to a common helper.

While here, also add a check to terminate in cases where the CPUID
function/subfunction is indexed and the subfunction is non-zero, since
the GHCB MSR protocol does not support non-zero subfunctions.

Suggested-by: Sean Christopherson <seanjc@google.com>
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/kernel/sev-shared.c | 83 +++++++++++++++++++++++-----------
arch/x86/kernel/sev.c | 1 +
3 files changed, 59 insertions(+), 26 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 485410a182b0..ed717b6dd246 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"
#include "../msr.h"
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 3aaef1a18ffe..b4d5558c9d0a 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -14,6 +14,16 @@
#define has_cpuflag(f) boot_cpu_has(f)
#endif

+/* I/O parameters for CPUID-related helpers */
+struct cpuid_leaf {
+ u32 fn;
+ u32 subfn;
+ u32 eax;
+ u32 ebx;
+ u32 ecx;
+ u32 edx;
+};
+
/*
* 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
@@ -194,6 +204,44 @@ enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb, bool set_ghcb_msr,
return verify_exception_info(ghcb, ctxt);
}

+static int __sev_cpuid_hv(u32 fn, int reg_idx, u32 *reg)
+{
+ u64 val;
+
+ sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, reg_idx));
+ VMGEXIT();
+ val = sev_es_rd_ghcb_msr();
+ if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
+ return -EIO;
+
+ *reg = (val >> 32);
+
+ return 0;
+}
+
+static int sev_cpuid_hv(struct cpuid_leaf *leaf)
+{
+ int ret;
+
+ /*
+ * MSR protocol does not support fetching non-zero subfunctions, but is
+ * sufficient to handle current early-boot cases. Should that change,
+ * make sure to report an error 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(leaf->fn) && leaf->subfn)
+ return -EINVAL;
+
+ ret = __sev_cpuid_hv(leaf->fn, GHCB_CPUID_REQ_EAX, &leaf->eax);
+ ret = ret ? : __sev_cpuid_hv(leaf->fn, GHCB_CPUID_REQ_EBX, &leaf->ebx);
+ ret = ret ? : __sev_cpuid_hv(leaf->fn, GHCB_CPUID_REQ_ECX, &leaf->ecx);
+ ret = ret ? : __sev_cpuid_hv(leaf->fn, GHCB_CPUID_REQ_EDX, &leaf->edx);
+
+ return ret;
+}
+
/*
* 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
@@ -201,40 +249,23 @@ enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb, bool set_ghcb_msr,
*/
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);
- unsigned long val;
+ struct cpuid_leaf leaf;

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

- sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EAX));
- VMGEXIT();
- val = sev_es_rd_ghcb_msr();
- if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
- goto fail;
- regs->ax = val >> 32;
-
- sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EBX));
- VMGEXIT();
- val = sev_es_rd_ghcb_msr();
- if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
- goto fail;
- regs->bx = val >> 32;
-
- sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_ECX));
- VMGEXIT();
- val = sev_es_rd_ghcb_msr();
- if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
+ leaf.fn = fn;
+ leaf.subfn = subfn;
+ if (sev_cpuid_hv(&leaf))
goto fail;
- regs->cx = val >> 32;

- sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EDX));
- VMGEXIT();
- val = sev_es_rd_ghcb_msr();
- if (GHCB_RESP_CODE(val) != GHCB_MSR_CPUID_RESP)
- goto fail;
- regs->dx = val >> 32;
+ regs->ax = leaf.eax;
+ regs->bx = leaf.ebx;
+ regs->cx = leaf.ecx;
+ regs->dx = leaf.edx;

/*
* This is a VC handler and the #VC is only raised when SEV-ES is
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index bc9bb7e0c04d..97c0aa44ce2d 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