Re: [PATCH v2] Livepatch for ARM 64 and 32.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Aug 31, 2016 at 09:54:30AM -0600, Jan Beulich wrote:
> >>> On 31.08.16 at 17:24, <andrew.cooper3@citrix.com> wrote:
> > On 31/08/16 16:09, Julien Grall wrote:
> >> On 31/08/16 16:06, Konrad Rzeszutek Wilk wrote:
> >>> So you are thinking of exposing this 'xen feature bits' that Andrew
> >>> mention
> >>> to be on ARM as well.
> >>
> >> I only chat with Andrew about it and I have not looked at the code, so
> >> I can't tell how it is on x86. I was just thinking to add LIVEPATCH
> >> bit in cpufeature.h for now and be worry later when cpufeature will be
> >> exposed to the toolstack for ARM.
> > 
> > Sorry - I have forgotten what exactly the purpose of this bit needs to
> > be, and therefore which bit of x86 I point you at.
> 
> I'm pretty sure talk here is about X86_FEATURE_ALWAYS.

Which is X86_FEATURE_LM, which is what we have in the test-case - and that
'lm' part is exposed to the toolstack.

Anyhow I believe Julien was thinking something like this:
(Would be nice if we could do arch-independent NOPs)

diff --git a/xen/arch/arm/livepatch.c b/xen/arch/arm/livepatch.c
index a076982..549f908 100644
--- a/xen/arch/arm/livepatch.c
+++ b/xen/arch/arm/livepatch.c
@@ -8,6 +8,7 @@
 #include <xen/livepatch.h>
 #include <xen/vmap.h>
 
+#include <asm/cpufeature.h>
 #include <asm/livepatch.h>
 #include <asm/mm.h>
 
@@ -167,6 +168,8 @@ void __init arch_livepatch_init(void)
     end = (void *)LIVEPATCH_VMAP_END;
 
     vm_init_type(VMAP_XEN, start, end);
+
+    cpus_set_cap(LIVEPATCH_FEATURE);
 }
 
 /*
diff --git a/xen/include/asm-arm/alternative.h b/xen/include/asm-arm/alternative.h
index 9f88fd9..074ff63 100644
--- a/xen/include/asm-arm/alternative.h
+++ b/xen/include/asm-arm/alternative.h
@@ -165,6 +165,8 @@ static inline int apply_alternatives(void *start, size_t lenght)
     return 0;
 }
 
+#define ALTERNATIVE(oldinstr, newinstr, ...) ""
+
 #endif
 
 #endif /* __ASM_ALTERNATIVE_H */
diff --git a/xen/include/asm-arm/cpufeature.h b/xen/include/asm-arm/cpufeature.h
index 66e930f..19e768b 100644
--- a/xen/include/asm-arm/cpufeature.h
+++ b/xen/include/asm-arm/cpufeature.h
@@ -40,7 +40,12 @@
 #define ARM32_WORKAROUND_766422 2
 #define ARM64_WORKAROUND_834220 3
 
+#ifdef CONFIG_LIVEPATCH
+#define LIVEPATCH_FEATURE   4
+#define ARM_NCAPS           5
+#else
 #define ARM_NCAPS           4
+#endif
 
 #ifndef __ASSEMBLY__
 
diff --git a/xen/include/asm-x86/cpufeature.h b/xen/include/asm-x86/cpufeature.h
index bcdf5d6..404dd91 100644
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -34,6 +34,7 @@ XEN_CPUFEATURE(MFENCE_RDTSC,    (FSCAPINTS+0)*32+ 9) /* MFENCE synchronizes RDTS
 
 /* An alias of a feature we know is always going to be present. */
 #define X86_FEATURE_ALWAYS      X86_FEATURE_LM
+#define LIVEPATCH_FEATURE       X86_FEATURE_ALWAYS
 
 #if !defined(__ASSEMBLY__) && !defined(X86_FEATURES_ONLY)
 #include <xen/bitops.h>
diff --git a/xen/test/livepatch/xen_hello_world_func.c b/xen/test/livepatch/xen_hello_world_func.c
index 6f53ab4..6b41a55 100644
--- a/xen/test/livepatch/xen_hello_world_func.c
+++ b/xen/test/livepatch/xen_hello_world_func.c
@@ -20,7 +20,6 @@ const char *xen_hello_world(void)
     unsigned long tmp;
     int rc;
 
-    alternative(ASM_NOP8, ASM_NOP1, X86_FEATURE_LM);
     /*
      * Any BUG, or WARN_ON will contain symbol and payload name. Furthermore
      * exceptions will be caught and processed properly.
@@ -28,8 +27,11 @@ const char *xen_hello_world(void)
     rc = __get_user(tmp, non_canonical_addr);
     BUG_ON(rc != -EFAULT);
 #endif
-#ifdef CONFIG_ARM_64
-    asm(ALTERNATIVE("nop", "nop", ARM64_WORKAROUND_CLEAN_CACHE));
+#ifdef CONFIG_ARM
+    asm(ALTERNATIVE("nop", "nop", LIVEPATCH_FEATURE));
+#endif
+#ifdef CONFIG_X86
+    asm(ALTERNATIVE(ASM_NOP8, ASM_NOP1, LIVEPATCH_FEATURE);
 #endif
     return "Hello World";
 }

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