From: "Daniel P. Smith" <dpsmith@apertussolutions.com>
To: Wei Liu <wl@xen.org>, xen-devel@lists.xenproject.org
Cc: "Andrew Cooper" <andrew.cooper3@citrix.com>,
"Jan Beulich" <jbeulich@suse.com>,
"Roger Pau Monné" <roger.pau@citrix.com>,
"George Dunlap" <george.dunlap@citrix.com>,
"Ian Jackson" <iwj@xenproject.org>,
"Julien Grall" <julien@xen.org>,
"Stefano Stabellini" <sstabellini@kernel.org>
Subject: [PATCH v2 01/10] xen: Implement xen/alternative-call.h for use in common code
Date: Mon, 12 Jul 2021 16:32:24 -0400 [thread overview]
Message-ID: <20210712203233.20289-2-dpsmith@apertussolutions.com> (raw)
In-Reply-To: <20210712203233.20289-1-dpsmith@apertussolutions.com>
From: Andrew Cooper <andrew.cooper3@citrix.com>
The alternative call infrastructure is x86-only for now, but the common iommu
code has a variant and more common code wants to use the infrastructure.
Introduce CONFIG_ALTERNATIVE_CALL and a conditional implemetnation so common
code can use the optimisation when available, without requiring all
architectures to implement no-op stubs.
Write some documentation, which was thus far entirely absent, covering the
requirements for an architecture to implement this optimsiation, and how to
use the infrastructure in general code.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
xen/arch/x86/Kconfig | 1 +
xen/common/Kconfig | 3 ++
xen/include/xen/alternative-call.h | 65 ++++++++++++++++++++++++++++++
3 files changed, 69 insertions(+)
create mode 100644 xen/include/xen/alternative-call.h
diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index 9b164db641..c91cdd83dc 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -9,6 +9,7 @@ config X86
select ARCH_SUPPORTS_INT128
select CORE_PARKING
select HAS_ALTERNATIVE
+ select ALTERNATIVE_CALL
select HAS_COMPAT
select HAS_CPUFREQ
select HAS_EHCI
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 0ddd18e11a..1594ce4e73 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -25,6 +25,9 @@ config GRANT_TABLE
config HAS_ALTERNATIVE
bool
+config ALTERNATIVE_CALL
+ bool
+
config HAS_COMPAT
bool
diff --git a/xen/include/xen/alternative-call.h b/xen/include/xen/alternative-call.h
new file mode 100644
index 0000000000..11d1c26068
--- /dev/null
+++ b/xen/include/xen/alternative-call.h
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef XEN_ALTERNATIVE_CALL
+#define XEN_ALTERNATIVE_CALL
+
+/*
+ * Some subsystems in Xen may have multiple implementions, which can be
+ * resolved to a single implementation at boot time. By default, this will
+ * result in the use of function pointers.
+ *
+ * Some architectures may have mechanisms for dynamically modifying .text.
+ * Using this mechnaism, function pointers can be converted to direct calls
+ * which are typically more efficient at runtime.
+ *
+ * For architectures to support:
+ *
+ * - Implement alternative_{,v}call() in asm/alternative.h. Code generation
+ * requirements are to emit a function pointer call at build time, and stash
+ * enough metadata to simplify the call at boot once the implementation has
+ * been resolved.
+ * - Select ALTERNATIVE_CALL in Kconfig.
+ *
+ * To use:
+ *
+ * Consider the following simplified example.
+ *
+ * 1) struct foo_ops __alt_call_maybe_initdata ops;
+ *
+ * 2) struct foo_ops __alt_call_maybe_initconst foo_a_ops = { ... };
+ * struct foo_ops __alt_call_maybe_initconst foo_b_ops = { ... };
+ *
+ * void foo_init(void)
+ * {
+ * ...
+ * if ( use_impl_a )
+ * ops = *foo_a_ops;
+ * else if ( use_impl_b )
+ * ops = *foo_b_ops;
+ * ...
+ * }
+ *
+ * 3) alternative_call(ops.bar, ...);
+ *
+ * There needs to a single ops object (1) which will eventually contain the
+ * function pointers. This should be populated in foo's init() function (2)
+ * by one of the available implementations. To call functions, use
+ * alternative_{,v}call() referencing the main ops object (3).
+ */
+
+#ifdef CONFIG_ALTERNATIVE_CALL
+
+#include <asm/alternative.h>
+
+#define __alt_call_maybe_initdata __initdata
+#define __alt_call_maybe_initconst __initconst
+
+#else
+
+#define alternative_call(func, args...) (func)(args)
+#define alternative_vcall(func, args...) (func)(args)
+
+#define __alt_call_maybe_initdata
+#define __alt_call_maybe_initconst
+
+#endif /* !CONFIG_ALTERNATIVE_CALL */
+#endif /* XEN_ALTERNATIVE_CALL */
--
2.20.1
next prev parent reply other threads:[~2021-07-12 20:27 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-12 20:32 [PATCH v2 00/10] xsm: refactoring xsm hooks Daniel P. Smith
2021-07-12 20:32 ` Daniel P. Smith [this message]
2021-07-12 23:48 ` [PATCH v2 01/10] xen: Implement xen/alternative-call.h for use in common code Andrew Cooper
2021-07-13 6:28 ` Jan Beulich
2021-07-13 8:36 ` Andrew Cooper
2021-07-13 8:53 ` Jan Beulich
2021-07-14 15:35 ` Jan Beulich
2021-07-12 20:32 ` [PATCH v2 02/10] xsm: refactor xsm_ops handling Daniel P. Smith
2021-07-12 23:39 ` Andrew Cooper
2021-07-14 15:54 ` Jan Beulich
2021-07-15 17:16 ` Daniel P. Smith
2021-07-12 20:32 ` [PATCH v2 03/10] xsm: remove the ability to disable flask Daniel P. Smith
2021-07-12 23:22 ` Andrew Cooper
2021-07-15 17:17 ` Daniel P. Smith
2021-07-14 15:58 ` Jan Beulich
2021-07-15 17:19 ` Daniel P. Smith
2021-07-12 20:32 ` [PATCH v2 04/10] xsm: convert xsm_ops hook calls to alternative call Daniel P. Smith
2021-07-12 23:44 ` Andrew Cooper
2021-07-15 17:20 ` Daniel P. Smith
2021-07-12 20:32 ` [PATCH v2 05/10] xsm: decouple xsm header inclusion selection Daniel P. Smith
2021-07-12 20:32 ` [PATCH v2 06/10] xsm: enable xsm to always be included Daniel P. Smith
2021-07-19 10:24 ` Jan Beulich
2021-07-25 20:47 ` Daniel P. Smith
2021-08-03 7:08 ` Jan Beulich
2021-07-12 20:32 ` [PATCH v2 07/10] xsm: drop generic event channel labeling Daniel P. Smith
2021-07-12 23:52 ` Andrew Cooper
2021-07-15 17:26 ` Daniel P. Smith
2021-07-16 7:03 ` Jan Beulich
2021-07-12 20:32 ` [PATCH v2 08/10] xsm: remove xsm_default_t from hook definitions Daniel P. Smith
2021-07-16 7:23 ` Jan Beulich
2021-07-16 14:15 ` Andrew Cooper
2021-07-16 14:55 ` Jan Beulich
2021-07-16 7:37 ` Jan Beulich
2021-07-27 13:39 ` Ian Jackson
2021-08-06 21:41 ` Daniel P. Smith
2021-08-10 8:39 ` Jan Beulich
2021-08-26 9:42 ` Jan Beulich
2021-07-12 20:32 ` [PATCH v2 09/10] xsm: expand the function related macros in dummy.h Daniel P. Smith
2021-07-16 7:34 ` Jan Beulich
2021-07-24 20:07 ` Daniel P. Smith
2021-07-24 20:43 ` Daniel P. Smith
2021-08-03 7:23 ` Jan Beulich
2021-07-12 20:32 ` [PATCH v2 10/10] xsm: removing the XSM_ASSERT_ACTION macro Daniel P. Smith
2021-07-12 23:12 ` [PATCH v2 00/10] xsm: refactoring xsm hooks Andrew Cooper
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