linux-kernel - [PATCH v3 05/10] x86/clearcpuid: Support multiple clearcpuid options

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Date:   Fri,  1 Feb 2019 21:14:46 -0800
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "H Peter Anvin" <hpa@...or.com>,
        "Dave Hansen" <dave.hansen@...el.com>,
        "Ashok Raj" <ashok.raj@...el.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Michael Chan" <michael.chan@...adcom.com>,
        "Ravi V Shankar" <ravi.v.shankar@...el.com>,
        "Ricardo Neri" <ricardo.neri@...el.com>
Cc:     "linux-kernel" <linux-kernel@...r.kernel.org>,
        "x86" <x86@...nel.org>, Fenghua Yu <fenghua.yu@...el.com>
Subject: [PATCH v3 05/10] x86/clearcpuid: Support multiple clearcpuid options

Currently only one kernel option "clearcpuid=" can be picked up by
kernel during boot time.

In some cases, user may want to clear a few cpu caps. This may be
useful to replace endless (new) kernel options like nosmep, nosmap,
etc.

We add support of multiple clearcpuid options to allow user to clear
multiple cpu caps.

Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
---
 arch/x86/include/asm/cmdline.h |  3 +++
 arch/x86/kernel/fpu/init.c     | 35 +++++++++++++++++++++++++----------
 arch/x86/lib/cmdline.c         | 17 +++++++++++++++--
 3 files changed, 43 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/cmdline.h b/arch/x86/include/asm/cmdline.h
index 6faaf27e8899..059e29558bb3 100644
--- a/arch/x86/include/asm/cmdline.h
+++ b/arch/x86/include/asm/cmdline.h
@@ -5,5 +5,8 @@
 int cmdline_find_option_bool(const char *cmdline_ptr, const char *option);
 int cmdline_find_option(const char *cmdline_ptr, const char *option,
 			char *buffer, int bufsize);
+int cmdline_find_option_in_range(const char *cmdline_ptr, int cmdline_size,
+				 const char *option, char *buffer, int bufsize,
+				 char **arg_pos);
 
 #endif /* _ASM_X86_CMDLINE_H */
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 6abd83572b01..da92f7f340c1 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -243,16 +243,36 @@ static void __init fpu__init_system_ctx_switch(void)
 	WARN_ON_FPU(current->thread.fpu.initialized);
 }
 
+static void __init setup_cpuid_option(char *setup_cpuid_option)
+{
+	void (*setup_cpu_cap)(unsigned int feature);
+	char arg[32], *argptr, *option_pos;
+	int bit, cmdline_size;
+
+	if (!strcmp(setup_cpuid_option, "clearcpuid"))
+		setup_cpu_cap = setup_clear_cpu_cap;
+		return;
+
+	/* Find each option in boot_command_line and clear specified cpu cap. */
+	cmdline_size = COMMAND_LINE_SIZE;
+	while (cmdline_find_option_in_range(boot_command_line, cmdline_size,
+					    setup_cpuid_option, arg,
+					    sizeof(arg), &option_pos) >= 0) {
+		/* Chang command line range for next search. */
+		cmdline_size = option_pos - boot_command_line + 1;
+		argptr = arg;
+		if (get_option(&argptr, &bit) &&
+		    bit >= 0 && bit < NCAPINTS * 32)
+			setup_cpu_cap(bit);
+	}
+}
+
 /*
  * We parse fpu parameters early because fpu__init_system() is executed
  * before parse_early_param().
  */
 static void __init fpu__init_parse_early_param(void)
 {
-	char arg[32];
-	char *argptr = arg;
-	int bit;
-
 	if (cmdline_find_option_bool(boot_command_line, "no387"))
 		setup_clear_cpu_cap(X86_FEATURE_FPU);
 
@@ -271,12 +291,7 @@ static void __init fpu__init_parse_early_param(void)
 	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
 		setup_clear_cpu_cap(X86_FEATURE_XSAVES);
 
-	if (cmdline_find_option(boot_command_line, "clearcpuid", arg,
-				sizeof(arg)) &&
-	    get_option(&argptr, &bit) &&
-	    bit >= 0 &&
-	    bit < NCAPINTS * 32)
-		setup_clear_cpu_cap(bit);
+	setup_cpuid_option("clearcpuid");
 }
 
 /*
diff --git a/arch/x86/lib/cmdline.c b/arch/x86/lib/cmdline.c
index 3261abb21ef4..9cf1a0773877 100644
--- a/arch/x86/lib/cmdline.c
+++ b/arch/x86/lib/cmdline.c
@@ -114,13 +114,15 @@ __cmdline_find_option_bool(const char *cmdline, int max_cmdline_size,
  * @option: option string to look for
  * @buffer: memory buffer to return the option argument
  * @bufsize: size of the supplied memory buffer
+ * @option_pos: pointer to the option if found
  *
  * Returns the length of the argument (regardless of if it was
  * truncated to fit in the buffer), or -1 on not found.
  */
 static int
 __cmdline_find_option(const char *cmdline, int max_cmdline_size,
-		      const char *option, char *buffer, int bufsize)
+		      const char *option, char *buffer, int bufsize,
+		      char **arg_pos)
 {
 	char c;
 	int pos = 0, len = -1;
@@ -164,6 +166,9 @@ __cmdline_find_option(const char *cmdline, int max_cmdline_size,
 				len = 0;
 				bufptr = buffer;
 				state = st_bufcpy;
+				if (arg_pos)
+					*arg_pos = (char *)cmdline -
+						   strlen(option) - 1;
 				break;
 			} else if (c == *opptr++) {
 				/*
@@ -211,5 +216,13 @@ int cmdline_find_option(const char *cmdline, const char *option, char *buffer,
 			int bufsize)
 {
 	return __cmdline_find_option(cmdline, COMMAND_LINE_SIZE, option,
-				     buffer, bufsize);
+				     buffer, bufsize, NULL);
+}
+
+int cmdline_find_option_in_range(const char *cmdline, int cmdline_size,
+				 char *option, char *buffer, int bufsize,
+				 char **arg_pos)
+{
+	return __cmdline_find_option(cmdline, cmdline_size, option, buffer,
+				     bufsize, arg_pos);
 }
-- 
2.7.4