Subject: [RFC PATCH V3 01/11] x86/HV: Initialize GHCB page in Isolation VM

From: Tianyu Lan <[email-masked]>
Date: Sun, 30 May 2021 11:06:18 -0400

From: Tianyu Lan <[email-masked]>

Hyper-V exposes GHCB page via SEV ES GHCB MSR for SNP guest
to communicate with hypervisor. Map GHCB page for all
cpus to read/write MSR register and submit hvcall request
via GHCB.

Signed-off-by: Tianyu Lan <[email-masked]>
---
 arch/x86/hyperv/hv_init.c       | 60 ++++++++++++++++++++++++++++++---
 arch/x86/include/asm/mshyperv.h |  2 ++
 include/asm-generic/mshyperv.h  |  2 ++
 3 files changed, 60 insertions(+), 4 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index bb0ae4b5c00f..dc74d01cb859 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -60,6 +60,9 @@ static int hv_cpu_init(unsigned int cpu)
 	struct hv_vp_assist_page **hvp = &hv_vp_assist_page[smp_processor_id()];
 	void **input_arg;
 	struct page *pg;
+	u64 ghcb_gpa;
+	void *ghcb_va;
+	void **ghcb_base;
 
 	/* hv_cpu_init() can be called with IRQs disabled from hv_resume() */
 	pg = alloc_pages(irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL, hv_root_partition ? 1 : 0);
@@ -106,6 +109,17 @@ static int hv_cpu_init(unsigned int cpu)
 		wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, val);
 	}
 
+	if (ms_hyperv.ghcb_base) {
+		rdmsrl(MSR_AMD64_SEV_ES_GHCB, ghcb_gpa);
+
+		ghcb_va = ioremap_cache(ghcb_gpa, HV_HYP_PAGE_SIZE);
+		if (!ghcb_va)
+			return -ENOMEM;
+
+		ghcb_base = (void **)this_cpu_ptr(ms_hyperv.ghcb_base);
+		*ghcb_base = ghcb_va;
+	}
+
 	return 0;
 }
 
@@ -201,6 +215,7 @@ static int hv_cpu_die(unsigned int cpu)
 	unsigned long flags;
 	void **input_arg;
 	void *pg;
+	void **ghcb_va = NULL;
 
 	local_irq_save(flags);
 	input_arg = (void **)this_cpu_ptr(hyperv_pcpu_input_arg);
@@ -214,6 +229,13 @@ static int hv_cpu_die(unsigned int cpu)
 		*output_arg = NULL;
 	}
 
+	if (ms_hyperv.ghcb_base) {
+		ghcb_va = (void **)this_cpu_ptr(ms_hyperv.ghcb_base);
+		if (*ghcb_va)
+			iounmap(*ghcb_va);
+		*ghcb_va = NULL;
+	}
+
 	local_irq_restore(flags);
 
 	free_pages((unsigned long)pg, hv_root_partition ? 1 : 0);
@@ -369,6 +391,9 @@ void __init hyperv_init(void)
 	u64 guest_id, required_msrs;
 	union hv_x64_msr_hypercall_contents hypercall_msr;
 	int cpuhp, i;
+	u64 ghcb_gpa;
+	void *ghcb_va;
+	void **ghcb_base;
 
 	if (x86_hyper_type != X86_HYPER_MS_HYPERV)
 		return;
@@ -429,9 +454,24 @@ void __init hyperv_init(void)
 			VMALLOC_END, GFP_KERNEL, PAGE_KERNEL_ROX,
 			VM_FLUSH_RESET_PERMS, NUMA_NO_NODE,
 			__builtin_return_address(0));
-	if (hv_hypercall_pg == NULL) {
-		wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
-		goto remove_cpuhp_state;
+	if (hv_hypercall_pg == NULL)
+		goto clean_guest_os_id;
+
+	if (hv_isolation_type_snp()) {
+		ms_hyperv.ghcb_base = alloc_percpu(void *);
+		if (!ms_hyperv.ghcb_base)
+			goto clean_guest_os_id;
+
+		rdmsrl(MSR_AMD64_SEV_ES_GHCB, ghcb_gpa);
+		ghcb_va = ioremap_cache(ghcb_gpa, HV_HYP_PAGE_SIZE);
+		if (!ghcb_va) {
+			free_percpu(ms_hyperv.ghcb_base);
+			ms_hyperv.ghcb_base = NULL;
+			goto clean_guest_os_id;
+		}
+
+		ghcb_base = (void **)this_cpu_ptr(ms_hyperv.ghcb_base);
+		*ghcb_base = ghcb_va;
 	}
 
 	rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
@@ -502,7 +542,8 @@ void __init hyperv_init(void)
 	hv_query_ext_cap(0);
 	return;
 
-remove_cpuhp_state:
+clean_guest_os_id:
+	wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
 	cpuhp_remove_state(cpuhp);
 free_vp_assist_page:
 	kfree(hv_vp_assist_page);
@@ -531,6 +572,9 @@ void hyperv_cleanup(void)
 	 */
 	hv_hypercall_pg = NULL;
 
+	if (ms_hyperv.ghcb_base)
+		free_percpu(ms_hyperv.ghcb_base);
+
 	/* Reset the hypercall page */
 	hypercall_msr.as_uint64 = 0;
 	wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
@@ -615,6 +659,14 @@ bool hv_is_isolation_supported(void)
 }
 EXPORT_SYMBOL_GPL(hv_is_isolation_supported);
 
+DEFINE_STATIC_KEY_FALSE(isolation_type_snp);
+
+bool hv_isolation_type_snp(void)
+{
+	return static_branch_unlikely(&isolation_type_snp);
+}
+EXPORT_SYMBOL_GPL(hv_isolation_type_snp);
+
 /* Bit mask of the extended capability to query: see HV_EXT_CAPABILITY_xxx */
 bool hv_query_ext_cap(u64 cap_query)
 {
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 67ff0d637e55..aeacca7c4da8 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -11,6 +11,8 @@
 #include <asm/paravirt.h>
 #include <asm/mshyperv.h>
 
+DECLARE_STATIC_KEY_FALSE(isolation_type_snp);
+
 typedef int (*hyperv_fill_flush_list_func)(
 		struct hv_guest_mapping_flush_list *flush,
 		void *data);
diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index 9a000ba2bb75..3ae56a29594f 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -35,6 +35,7 @@ struct ms_hyperv_info {
 	u32 max_lp_index;
 	u32 isolation_config_a;
 	u32 isolation_config_b;
+	void  __percpu **ghcb_base;
 };
 extern struct ms_hyperv_info ms_hyperv;
 
@@ -224,6 +225,7 @@ bool hv_is_hyperv_initialized(void);
 bool hv_is_hibernation_supported(void);
 enum hv_isolation_type hv_get_isolation_type(void);
 bool hv_is_isolation_supported(void);
+bool hv_isolation_type_snp(void);
 void hyperv_cleanup(void);
 bool hv_query_ext_cap(u64 cap_query);
 #else /* CONFIG_HYPERV */
-- 
2.25.1