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Date:   Thu, 25 Jun 2020 12:53:55 +0100
From:   David Brazdil <dbrazdil@google.com>
To:     Marc Zyngier <maz@kernel.org>
Cc:     Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        James Morse <james.morse@arm.com>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, android-kvm@google.com,
        kernel-team@android.com
Subject: Re: [PATCH v3 05/15] arm64: kvm: Build hyp-entry.S separately for
 VHE/nVHE
Message-ID: <20200625115355.iqt3np4m6gjmpbap@google.com>
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 <5029f8fb4a7816e11de7469c09347c79@kernel.org>
 <20200622102041.myve2otyoj5q7j5s@google.com>
 <491f3c8877897a4ac69d69fb7354c1cb@kernel.org>
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Hey Marc,

> I'd be happy with the (maybe temporary) magic approach. It helps reasoning
> about things, and makes the transition smoother. Yes, bugs could crop up
> there, but given the static nature of obtaining a symbol's address, I'm
> fairly confident we'll get it right. The same cannot be said about pointers
> though.

Ok, so this is what it would look like:

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 6a682d66a640..0d1b3b1946f0 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -59,13 +59,14 @@
 #define DECLARE_KVM_HYP_SYM(sym)               \
        DECLARE_KVM_VHE_SYM(sym);               \
        DECLARE_KVM_NVHE_SYM(sym)
+#define CHOOSE_HYP_SYM(sym) (has_vhe() ? sym : kvm_nvhe_sym(sym))

 /* Translate a kernel address of @sym into its equivalent linear mapping */
-#define kvm_ksym_ref(sym)                                              \
+#define kvm_ksym_ref(ptr)                                              \
        ({                                                              \
-               void *val = &sym;                                       \
+               void *val = (ptr);                                      \
                if (!is_kernel_in_hyp_mode())                           \
-                       val = lm_alias(&sym);                           \
+                       val = lm_alias((ptr));                          \
                val;                                                    \
         })
 #define kvm_ksym_ref_nvhe(sym) kvm_ksym_ref(kvm_nvhe_sym(sym))
@@ -76,7 +77,14 @@ struct kvm_vcpu;
 extern char __kvm_hyp_init[];
 extern char __kvm_hyp_init_end[];

-extern char __kvm_hyp_vector[];
+DECLARE_KVM_HYP_SYM(__kvm_hyp_vector);
+#define __kvm_hyp_vector CHOOSE_HYP_SYM(__kvm_hyp_vector)
+
+#ifdef CONFIG_KVM_INDIRECT_VECTORS
+DECLARE_KVM_HYP_SYM(__bp_harden_hyp_vecs);
+#define __bp_harden_hyp_vecs CHOOSE_HYP_SYM(__bp_harden_hyp_vecs)
+extern atomic_t arm64_el2_vector_last_slot;
+#endif

 extern void __kvm_flush_vm_context(void);
 extern void __kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa);

Everything compiles and boots. Only existing code I had to change was:

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 90cb90561446..34b551385153 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1285,7 +1285,7 @@ static void cpu_init_hyp_mode(void)
         * so that we can use adr_l to access per-cpu variables in EL2.
         */
        tpidr_el2 = ((unsigned long)this_cpu_ptr(&kvm_host_data) -
-                    (unsigned long)kvm_ksym_ref(kvm_host_data));
+                    (unsigned long)kvm_ksym_ref(&kvm_host_data));

        pgd_ptr = kvm_mmu_get_httbr();
        hyp_stack_ptr = __this_cpu_read(kvm_arm_hyp_stack_page) + PAGE_SIZE;

WDYT?

Thanks,
-David