On Mon, Jan 14, 2013 at 10:11 AM, Will Deacon [off-list ref] wrote:

On Tue, Jan 08, 2013 at 06:39:03PM +0000, Christoffer Dall wrote:

quoted

Sets up KVM code to handle all exceptions taken to Hyp mode.

When the kernel is booted in Hyp mode, calling an hvc instruction with r0
pointing to the new vectors, the HVBAR is changed to the the vector pointers.
This allows subsystems (like KVM here) to execute code in Hyp-mode with the
MMU disabled.

We initialize other Hyp-mode registers and enables the MMU for Hyp-mode from
the id-mapped hyp initialization code. Afterwards, the HVBAR is changed to
point to KVM Hyp vectors used to catch guest faults and to switch to Hyp mode
to perform a world-switch into a KVM guest.

Also provides memory mapping code to map required code pages, data structures,
and I/O regions  accessed in Hyp mode at the same virtual address as the host
kernel virtual addresses, but which conforms to the architectural requirements
for translations in Hyp mode. This interface is added in arch/arm/kvm/arm_mmu.c
and comprises:
 - create_hyp_mappings(from, to);
 - create_hyp_io_mappings(from, to, phys_addr);
 - free_hyp_pmds();

[...]

quoted

diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 82cb338..2dddc58 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c

@@ -34,11 +34,21 @@
 #include <asm/ptrace.h>
 #include <asm/mman.h>
 #include <asm/cputype.h>
+#include <asm/tlbflush.h>
+#include <asm/virt.h>
+#include <asm/kvm_arm.h>
+#include <asm/kvm_asm.h>
+#include <asm/kvm_mmu.h>

 #ifdef REQUIRES_VIRT
 __asm__(".arch_extension       virt");
 #endif

+static DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
+static struct vfp_hard_struct __percpu *kvm_host_vfp_state;
+static unsigned long hyp_default_vectors;
+
+
 int kvm_arch_hardware_enable(void *garbage)
 {
        return 0;

@@ -336,9 +346,176 @@ long kvm_arch_vm_ioctl(struct file *filp,
        return -EINVAL;
 }

+static void cpu_init_hyp_mode(void *vector)
+{
+       unsigned long long pgd_ptr;
+       unsigned long hyp_stack_ptr;
+       unsigned long stack_page;
+       unsigned long vector_ptr;
+
+       /* Switch from the HYP stub to our own HYP init vector */
+       __hyp_set_vectors((unsigned long)vector);
+
+       pgd_ptr = (unsigned long long)kvm_mmu_get_httbr();
+       stack_page = __get_cpu_var(kvm_arm_hyp_stack_page);
+       hyp_stack_ptr = stack_page + PAGE_SIZE;
+       vector_ptr = (unsigned long)__kvm_hyp_vector;
+
+       /*
+        * Call initialization code, and switch to the full blown
+        * HYP code. The init code corrupts r12, so set the clobber
+        * list accordingly.
+        */
+       asm volatile (
+               "mov    r0, %[pgd_ptr_low]\n\t"
+               "mov    r1, %[pgd_ptr_high]\n\t"
+               "mov    r2, %[hyp_stack_ptr]\n\t"
+               "mov    r3, %[vector_ptr]\n\t"
+               "hvc    #0\n\t" : :
+               [pgd_ptr_low] "r" ((unsigned long)(pgd_ptr & 0xffffffff)),
+               [pgd_ptr_high] "r" ((unsigned long)(pgd_ptr >> 32ULL)),
+               [hyp_stack_ptr] "r" (hyp_stack_ptr),
+               [vector_ptr] "r" (vector_ptr) :
+               "r0", "r1", "r2", "r3", "r12");
+}

Use kvm_call_hyp here instead.

good idea:

commit 00e22196205800ce9caa561e7c806023f4915138
Author: Christoffer Dall [off-list ref]
Date:   Mon Jan 14 11:32:36 2013 -0500

    KVM: ARM: Reuse kvm_call_hyp in vcpu_init_hyp_mode

    Instead of directly and manually callin the hypercall into the KVM init
    code, use the kvm_call_hyp function, which only requires a small abuse
    of the prototype in exchange for much nicer C code.

    Cc: Will Deacon [off-list ref]
    Signed-off-by: Christoffer Dall [off-list ref]

diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 6997326..b5c6ab1 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c

@@ -971,6 +971,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
 static void cpu_init_hyp_mode(void *vector)
 {
 	unsigned long long pgd_ptr;
+	unsigned long pgd_low, pgd_high;
 	unsigned long hyp_stack_ptr;
 	unsigned long stack_page;
 	unsigned long vector_ptr;

@@ -979,26 +980,20 @@ static void cpu_init_hyp_mode(void *vector)
 	__hyp_set_vectors((unsigned long)vector);

 	pgd_ptr = (unsigned long long)kvm_mmu_get_httbr();
+	pgd_low = (pgd_ptr & ((1ULL << 32) - 1));
+	pgd_high = (pgd_ptr >> 32ULL);
 	stack_page = __get_cpu_var(kvm_arm_hyp_stack_page);
 	hyp_stack_ptr = stack_page + PAGE_SIZE;
 	vector_ptr = (unsigned long)__kvm_hyp_vector;

 	/*
 	 * Call initialization code, and switch to the full blown
-	 * HYP code. The init code corrupts r12, so set the clobber
-	 * list accordingly.
+	 * HYP code. The init code doesn't need to preserve these registers as
+	 * r1-r3 and r12 are already callee save according to the AAPCS.
+	 * Note that we slightly misuse the prototype by casing the pgd_low to
+	 * a void *.
 	 */
-	asm volatile (
-		"mov	r0, %[pgd_ptr_low]\n\t"
-		"mov	r1, %[pgd_ptr_high]\n\t"
-		"mov	r2, %[hyp_stack_ptr]\n\t"
-		"mov	r3, %[vector_ptr]\n\t"
-		"hvc	#0\n\t" : :
-		[pgd_ptr_low] "r" ((unsigned long)(pgd_ptr & 0xffffffff)),
-		[pgd_ptr_high] "r" ((unsigned long)(pgd_ptr >> 32ULL)),
-		[hyp_stack_ptr] "r" (hyp_stack_ptr),
-		[vector_ptr] "r" (vector_ptr) :
-		"r0", "r1", "r2", "r3", "r12");
+	kvm_call_hyp((void *)pgd_low, pgd_high, hyp_stack_ptr, vector_ptr);
 }

 /**
--

Thanks,
-Christoffer