[xen master] xen: Introduce cmpxchg64() and guest_cmpxchg64()

[patchbot@xxxxxxx]

commit c729d54331ffb05abe93ed2349377092f134fdbd
Author:     Julien Grall <jgrall@xxxxxxxxxx>
AuthorDate: Fri Sep 11 17:06:22 2020 +0100
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Fri Sep 18 17:33:01 2020 +0100

    xen: Introduce cmpxchg64() and guest_cmpxchg64()
    
    The IOREQ code is using cmpxchg() with 64-bit value. At the moment, this
    is x86 code, but there is plan to make it common.
    
    To cater 32-bit arch, introduce two new helpers to deal with 64-bit
    cmpxchg().
    
    The Arm 32-bit implementation of cmpxchg64() is based on the __cmpxchg64
    in Linux v5.8 (arch/arm/include/asm/cmpxchg.h).
    
    Note that only guest_cmpxchg64() is introduced on x86 so far.
    
    Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/include/asm-arm/arm32/cmpxchg.h | 68 +++++++++++++++++++++++++++++++++++++
 xen/include/asm-arm/arm64/cmpxchg.h |  5 +++
 xen/include/asm-arm/guest_atomics.h | 22 ++++++++++++
 xen/include/asm-x86/guest_atomics.h |  1 +
 4 files changed, 96 insertions(+)

diff --git a/xen/include/asm-arm/arm32/cmpxchg.h 
b/xen/include/asm-arm/arm32/cmpxchg.h
index 3ef1e5c632..b0bd1d8b68 100644
--- a/xen/include/asm-arm/arm32/cmpxchg.h
+++ b/xen/include/asm-arm/arm32/cmpxchg.h
@@ -87,6 +87,37 @@ __CMPXCHG_CASE(b, 1)
 __CMPXCHG_CASE(h, 2)
 __CMPXCHG_CASE( , 4)
 
+static inline bool __cmpxchg_case_8(volatile uint64_t *ptr,
+                                   uint64_t *old,
+                                   uint64_t new,
+                                   bool timeout,
+                                   unsigned int max_try)
+{
+       uint64_t oldval;
+       uint64_t res;
+
+       do {
+               asm volatile(
+               "       ldrexd          %1, %H1, [%3]\n"
+               "       teq             %1, %4\n"
+               "       teqeq           %H1, %H4\n"
+               "       movne           %0, #0\n"
+               "       movne           %H0, #0\n"
+               "       bne             2f\n"
+               "       strexd          %0, %5, %H5, [%3]\n"
+               "2:"
+               : "=&r" (res), "=&r" (oldval), "+Qo" (*ptr)
+               : "r" (ptr), "r" (*old), "r" (new)
+               : "memory", "cc");
+               if (!res)
+                       break;
+       } while (!timeout || ((--max_try) > 0));
+
+       *old = oldval;
+
+       return !res;
+}
+
 static always_inline bool __int_cmpxchg(volatile void *ptr, unsigned long *old,
                                        unsigned long new, int size,
                                        bool timeout, unsigned int max_try)
@@ -145,11 +176,48 @@ static always_inline bool __cmpxchg_timeout(volatile void 
*ptr,
        return ret;
 }
 
+/*
+ * The helper may fail to update the memory if the action takes too long.
+ *
+ * @old: On call the value pointed contains the expected old value. It will be
+ * updated to the actual old value.
+ * @max_try: Maximum number of iterations
+ *
+ * The helper will return true when the update has succeeded (i.e no
+ * timeout) and false if the update has failed.
+ */
+static always_inline bool __cmpxchg64_timeout(volatile uint64_t *ptr,
+                                             uint64_t *old,
+                                             uint64_t new,
+                                             unsigned int max_try)
+{
+       bool ret;
+
+       smp_mb();
+       ret = __cmpxchg_case_8(ptr, old, new, true, max_try);
+       smp_mb();
+
+       return ret;
+}
+
 #define cmpxchg(ptr,o,n)                                               \
        ((__typeof__(*(ptr)))__cmpxchg((ptr),                           \
                                       (unsigned long)(o),              \
                                       (unsigned long)(n),              \
                                       sizeof(*(ptr))))
+
+static inline uint64_t cmpxchg64(volatile uint64_t *ptr,
+                                uint64_t old,
+                                uint64_t new)
+{
+       smp_mb();
+       if (!__cmpxchg_case_8(ptr, &old, new, false, 0))
+               ASSERT_UNREACHABLE();
+       smp_mb();
+
+       return old;
+}
+
 #endif
 /*
  * Local variables:
diff --git a/xen/include/asm-arm/arm64/cmpxchg.h 
b/xen/include/asm-arm/arm64/cmpxchg.h
index f4a8c1ccba..10e4edc022 100644
--- a/xen/include/asm-arm/arm64/cmpxchg.h
+++ b/xen/include/asm-arm/arm64/cmpxchg.h
@@ -167,6 +167,11 @@ static always_inline bool __cmpxchg_timeout(volatile void 
*ptr,
        __ret; \
 })
 
+#define cmpxchg64(ptr, o, n) cmpxchg(ptr, o, n)
+
+#define __cmpxchg64_timeout(ptr, old, new, max_try)    \
+       __cmpxchg_timeout(ptr, old, new, 8, max_try)
+
 #endif
 /*
  * Local variables:
diff --git a/xen/include/asm-arm/guest_atomics.h 
b/xen/include/asm-arm/guest_atomics.h
index 20347849e5..9e2e96d4ff 100644
--- a/xen/include/asm-arm/guest_atomics.h
+++ b/xen/include/asm-arm/guest_atomics.h
@@ -115,6 +115,28 @@ static inline unsigned long __guest_cmpxchg(struct domain 
*d,
                                          (unsigned long)(n),\
                                          sizeof (*(ptr))))
 
+static inline uint64_t guest_cmpxchg64(struct domain *d,
+                                       volatile uint64_t *ptr,
+                                       uint64_t old,
+                                       uint64_t new)
+{
+    uint64_t oldval = old;
+
+    perfc_incr(atomics_guest);
+
+    if ( __cmpxchg64_timeout(ptr, &oldval, new,
+                             this_cpu(guest_safe_atomic_max)) )
+        return oldval;
+
+    perfc_incr(atomics_guest_paused);
+
+    domain_pause_nosync(d);
+    oldval = cmpxchg64(ptr, old, new);
+    domain_unpause(d);
+
+    return oldval;
+}
+
 #endif /* _ARM_GUEST_ATOMICS_H */
 /*
  * Local variables:
diff --git a/xen/include/asm-x86/guest_atomics.h 
b/xen/include/asm-x86/guest_atomics.h
index 029417c8ff..c2dec0d650 100644
--- a/xen/include/asm-x86/guest_atomics.h
+++ b/xen/include/asm-x86/guest_atomics.h
@@ -20,6 +20,7 @@
     ((void)(d), test_and_change_bit(nr, p))
 
 #define guest_cmpxchg(d, ptr, o, n) ((void)(d), cmpxchg(ptr, o, n))
+#define guest_cmpxchg64 guest_cmpxchg
 
 #endif /* _X86_GUEST_ATOMICS_H */
 /*
--
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