Re: [PATCH v1 1/4] x86/fred: Parse cmdline param "fred=" in cpu_parse_early_param()

From: Xin Li
Date: Sun Jul 07 2024 - 13:43:32 EST


On 7/4/2024 4:20 AM, Nikolay Borisov wrote:


On 3.07.24 г. 11:54 ч., Xin Li (Intel) wrote:
Depending on whether FRED will be used, sysvec_install() installs
a system interrupt handler into FRED system vector dispatch table
or IDT.  However FRED can be disabled later in trap_init(), after
sysvec_install() is called.  E.g., the HYPERVISOR_CALLBACK_VECTOR
handler is registered with sysvec_install() in kvm_guest_init(),
which is called in setup_arch() but way before trap_init().  IOW,
there is a gap between FRED is available and available but disabled.
As a result, when FRED is available but disabled, its IDT handler
is not installed thus spurious_interrupt() will be invoked.

Fix it by parsing cmdline param "fred=" in cpu_parse_early_param()
to minimize the gap between FRED is available and available but
disabled.

Fixes: 3810da12710a ("x86/fred: Add a fred= cmdline param")
Reported-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Xin Li (Intel) <xin@xxxxxxxxx>
---
  arch/x86/kernel/cpu/common.c |  5 +++++
  arch/x86/kernel/traps.c      | 26 --------------------------
  2 files changed, 5 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index d4e539d4e158..9a904fe7c829 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1510,6 +1510,11 @@ static void __init cpu_parse_early_param(void)
      if (cmdline_find_option_bool(boot_command_line, "nousershstk"))
          setup_clear_cpu_cap(X86_FEATURE_USER_SHSTK);
+    /* Minimize the gap between FRED is available and available but disabled. */
+    arglen = cmdline_find_option(boot_command_line, "fred", arg, sizeof(arg));
+    if (arglen != strlen("on") || strcmp(arg, "on"))


Just make this check :

ret = cmdline_find_option(...)
if (ret < 0 || strcmp()))

A lot more straightforward


I'd do
if (arglen != 2 || strncmp(arg, "on", 2))

If arglen is 2, strncmp(arg, "on", 2) is essentially strcmp(arg, "on"), but I should've kept using strncmp.