[Xen-devel] [PATCH] xen/tasklet: Fix return value truncation on arm64

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

The use of return_reg() assumes ARM's 32bit ABI.  Therefore, a failure such as
-EINVAL will appear as a large positive number near 4 billion to a 64bit ARM
guest which happens to use continue_hypercall_on_cpu().

Introduce a new arch_hypercall_tasklet_result() hook which is implemented by
both architectures, and drop the return_reg() macros.  This logic will be
extended in a later change to make continuations out of the tasklet work.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>

This has been build tested on ARM, and functionally tested on x86.  It is
broken out of the larger continuation series partly because it is ready, and
partly because I wanted a simple change to try patchew with.

I also note that it is very rude of this logic to fail the hypercall with
-EINVAL when it misses the correct CPU.  This bug is also fixed by the later
continuation work.
---
 xen/arch/arm/traps.c       | 7 +++++++
 xen/arch/x86/hypercall.c   | 7 +++++++
 xen/common/domain.c        | 9 +++++++--
 xen/include/asm-arm/regs.h | 2 --
 xen/include/asm-x86/regs.h | 2 --
 xen/include/xen/domain.h   | 6 ++++++
 6 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index d8b9a8a..c4ae877 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1510,6 +1510,13 @@ static void do_trap_hypercall(struct cpu_user_regs 
*regs, register_t *nr,
         regs->pc -= 4;  /* re-execute 'hvc #XEN_HYPERCALL_TAG' */
 }
 
+void arch_hypercall_tasklet_result(struct vcpu *v, long res)
+{
+    struct cpu_user_regs *regs = &v->arch.cpu_info->guest_cpu_user_regs;
+
+    HYPERCALL_RESULT_REG(regs) = res;
+}
+
 static bool check_multicall_32bit_clean(struct multicall_entry *multi)
 {
     int i;
diff --git a/xen/arch/x86/hypercall.c b/xen/arch/x86/hypercall.c
index cf44b82..c770bae 100644
--- a/xen/arch/x86/hypercall.c
+++ b/xen/arch/x86/hypercall.c
@@ -157,6 +157,13 @@ unsigned long hypercall_create_continuation(
     return op;
 }
 
+void arch_hypercall_tasklet_result(struct vcpu *v, long res)
+{
+    struct cpu_user_regs *regs = &v->arch.user_regs;
+
+    regs->rax = res;
+}
+
 int hypercall_xlat_continuation(unsigned int *id, unsigned int nr,
                                 unsigned int mask, ...)
 {
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 88bbe98..50aa67f 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1619,13 +1619,18 @@ static void continue_hypercall_tasklet_handler(unsigned 
long _info)
 {
     struct migrate_info *info = (struct migrate_info *)_info;
     struct vcpu *v = info->vcpu;
+    long res = -EINVAL;
 
     /* Wait for vcpu to sleep so that we can access its register state. */
     vcpu_sleep_sync(v);
 
     this_cpu(continue_info) = info;
-    return_reg(v) = (info->cpu == smp_processor_id())
-        ? info->func(info->data) : -EINVAL;
+
+    if ( likely(info->cpu == smp_processor_id()) )
+        res = info->func(info->data);
+
+    arch_hypercall_tasklet_result(v, res);
+
     this_cpu(continue_info) = NULL;
 
     if ( info->nest-- == 0 )
diff --git a/xen/include/asm-arm/regs.h b/xen/include/asm-arm/regs.h
index ddc6eba..e3ea8a4 100644
--- a/xen/include/asm-arm/regs.h
+++ b/xen/include/asm-arm/regs.h
@@ -50,8 +50,6 @@ static inline bool guest_mode(const struct cpu_user_regs *r)
     return (diff == 0);
 }
 
-#define return_reg(v) ((v)->arch.cpu_info->guest_cpu_user_regs.r0)
-
 register_t get_user_reg(struct cpu_user_regs *regs, int reg);
 void set_user_reg(struct cpu_user_regs *regs, int reg, register_t val);
 
diff --git a/xen/include/asm-x86/regs.h b/xen/include/asm-x86/regs.h
index 725a664..dc00b85 100644
--- a/xen/include/asm-x86/regs.h
+++ b/xen/include/asm-x86/regs.h
@@ -15,6 +15,4 @@
     (diff == 0);                                                              \
 })
 
-#define return_reg(v) ((v)->arch.user_regs.rax)
-
 #endif /* __X86_REGS_H__ */
diff --git a/xen/include/xen/domain.h b/xen/include/xen/domain.h
index d1bfc82..3cb7f0a 100644
--- a/xen/include/xen/domain.h
+++ b/xen/include/xen/domain.h
@@ -102,6 +102,12 @@ void domctl_lock_release(void);
 int continue_hypercall_on_cpu(
     unsigned int cpu, long (*func)(void *data), void *data);
 
+/*
+ * Companion to continue_hypercall_on_cpu(), to feed func()'s result back into
+ * vcpu regsiter state.
+ */
+void arch_hypercall_tasklet_result(struct vcpu *v, long res);
+
 extern unsigned int xen_processor_pmbits;
 
 extern bool_t opt_dom0_vcpus_pin;
-- 
2.1.4


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel