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

Nikolay Borisov
2024-07-04T11:20:24Z

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@antgroup.com>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Xin Li (Intel) <xin@zytor.com>
> ---
> 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

> + setup_clear_cpu_cap(X86_FEATURE_FRED);
> +
> arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
> if (arglen <= 0)
> return;
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 4fa0b17e5043..6afb41e6cbbb 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -1402,34 +1402,8 @@ DEFINE_IDTENTRY_SW(iret_error)
> }
> #endif
>
> -/* Do not enable FRED by default yet. */
> -static bool enable_fred __ro_after_init = false;
> -
> -#ifdef CONFIG_X86_FRED
> -static int __init fred_setup(char *str)
> -{
> - if (!str)
> - return -EINVAL;
> -
> - if (!cpu_feature_enabled(X86_FEATURE_FRED))
> - return 0;
> -
> - if (!strcmp(str, "on"))
> - enable_fred = true;
> - else if (!strcmp(str, "off"))
> - enable_fred = false;
> - else
> - pr_warn("invalid FRED option: 'fred=%s'\n", str);
> - return 0;
> -}
> -early_param("fred", fred_setup);
> -#endif
> -
> void __init trap_init(void)
> {
> - if (cpu_feature_enabled(X86_FEATURE_FRED) && !enable_fred)
> - setup_clear_cpu_cap(X86_FEATURE_FRED);
> -
> /* Init cpu_entry_area before IST entries are set up */
> setup_cpu_entry_areas();
>