[PATCH v2 4/5] KVM: arm64: Allocate shared stacktrace pages

[Kalesh Singh]

The nVHE hypervisor can use this shared area to dump its stacktrace
addresses on hyp_panic(). Symbolization and printing the stacktrace can
then be handled by the host in EL1 (done in a later patch in this series).

Signed-off-by: Kalesh Singh <kaleshsingh at google.com>
---
 arch/arm64/include/asm/kvm_asm.h |  1 +
 arch/arm64/kvm/arm.c             | 34 ++++++++++++++++++++++++++++++++
 arch/arm64/kvm/hyp/nvhe/setup.c  | 11 +++++++++++
 3 files changed, 46 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 2e277f2ed671..ad31ac68264f 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -174,6 +174,7 @@ struct kvm_nvhe_init_params {
 	unsigned long hcr_el2;
 	unsigned long vttbr;
 	unsigned long vtcr;
+	unsigned long stacktrace_hyp_va;
 };
 
 /* Translate a kernel address @ptr into its equivalent linear mapping */
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index d300def44f5c..26005182da20 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -50,6 +50,7 @@ DEFINE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
 DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
 
 static DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
+DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stacktrace_page);
 unsigned long kvm_arm_hyp_percpu_base[NR_CPUS];
 DECLARE_KVM_NVHE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
 
@@ -1484,6 +1485,7 @@ static void cpu_prepare_hyp_mode(int cpu)
 	tcr |= (idmap_t0sz & GENMASK(TCR_TxSZ_WIDTH - 1, 0)) << TCR_T0SZ_OFFSET;
 	params->tcr_el2 = tcr;
 
+	params->stacktrace_hyp_va = kern_hyp_va(per_cpu(kvm_arm_hyp_stacktrace_page, cpu));
 	params->pgd_pa = kvm_mmu_get_httbr();
 	if (is_protected_kvm_enabled())
 		params->hcr_el2 = HCR_HOST_NVHE_PROTECTED_FLAGS;
@@ -1777,6 +1779,7 @@ static void teardown_hyp_mode(void)
 	free_hyp_pgds();
 	for_each_possible_cpu(cpu) {
 		free_page(per_cpu(kvm_arm_hyp_stack_page, cpu));
+		free_page(per_cpu(kvm_arm_hyp_stacktrace_page, cpu));
 		free_pages(kvm_arm_hyp_percpu_base[cpu], nvhe_percpu_order());
 	}
 }
@@ -1868,6 +1871,23 @@ static int init_hyp_mode(void)
 		per_cpu(kvm_arm_hyp_stack_page, cpu) = stack_page;
 	}
 
+	/*
+	 * Allocate stacktrace pages for Hypervisor-mode.
+	 * This is used by the hypervisor to share its stacktrace
+	 * with the host on a hyp_panic().
+	 */
+	for_each_possible_cpu(cpu) {
+		unsigned long stacktrace_page;
+
+		stacktrace_page = __get_free_page(GFP_KERNEL);
+		if (!stacktrace_page) {
+			err = -ENOMEM;
+			goto out_err;
+		}
+
+		per_cpu(kvm_arm_hyp_stacktrace_page, cpu) = stacktrace_page;
+	}
+
 	/*
 	 * Allocate and initialize pages for Hypervisor-mode percpu regions.
 	 */
@@ -1975,6 +1995,20 @@ static int init_hyp_mode(void)
 		params->stack_hyp_va = hyp_addr + (2 * PAGE_SIZE);
 	}
 
+	/*
+	 * Map the hyp stacktrace pages.
+	 */
+	for_each_possible_cpu(cpu) {
+		char *stacktrace_page = (char *)per_cpu(kvm_arm_hyp_stacktrace_page, cpu);
+
+		err = create_hyp_mappings(stacktrace_page, stacktrace_page + PAGE_SIZE,
+					  PAGE_HYP);
+		if (err) {
+			kvm_err("Cannot map hyp stacktrace page\n");
+			goto out_err;
+		}
+	}
+
 	for_each_possible_cpu(cpu) {
 		char *percpu_begin = (char *)kvm_arm_hyp_percpu_base[cpu];
 		char *percpu_end = percpu_begin + nvhe_percpu_size();
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index e8d4ea2fcfa0..9b81bf2d40d7 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -135,6 +135,17 @@ static int recreate_hyp_mappings(phys_addr_t phys, unsigned long size,
 
 		/* Update stack_hyp_va to end of the stack's private VA range */
 		params->stack_hyp_va = hyp_addr + (2 * PAGE_SIZE);
+
+		/*
+		 * Map the stacktrace pages as shared and transfer ownership to
+		 * the hypervisor.
+		 */
+		prot = pkvm_mkstate(PAGE_HYP, PKVM_PAGE_SHARED_OWNED);
+		start = (void *)params->stacktrace_hyp_va;
+		end = start + PAGE_SIZE;
+		ret = pkvm_create_mappings(start, end, prot);
+		if (ret)
+			return ret;
 	}
 
 	/*
-- 
2.36.0.464.gb9c8b46e94-goog