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

[Xin Li]

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.