[Xen-changelog] [xen staging] xen/tasklet: Fix return value truncation on arm64

[patchbot@xxxxxxx]

commit 08aa26349a5262563f0b8f69b08a67e2c4999410
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Apr 11 13:54:36 2019 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Dec 27 17:18:57 2019 +0000

    xen/tasklet: Fix return value truncation on arm64
    
    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>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Julien Grall <julien@xxxxxxx>
---
 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 d028ec9224..a20474f87c 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1485,6 +1485,13 @@ 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 1d42702c6a..7f299d45c6 100644
--- a/xen/arch/x86/hypercall.c
+++ b/xen/arch/x86/hypercall.c
@@ -166,6 +166,13 @@ unsigned long hypercall_create_continuation(
 
 #undef NEXT_ARG
 
+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 611116c7fc..ccf689fcbe 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1665,13 +1665,18 @@ 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 0e3e56b452..ec091a28a2 100644
--- a/xen/include/asm-arm/regs.h
+++ b/xen/include/asm-arm/regs.h
@@ -57,8 +57,6 @@ 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 725a664e0a..dc00b854e3 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 769302057b..1cb205d977 100644
--- a/xen/include/xen/domain.h
+++ b/xen/include/xen/domain.h
@@ -103,6 +103,12 @@ 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;
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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