Messages in this thread | | | Date | Mon, 21 Aug 2023 09:17:06 -0700 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 01/22] x86/srso: Fix srso_show_state() side effect |
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On Mon, Aug 21, 2023 at 08:04:16AM +0200, Borislav Petkov wrote: > On Sun, Aug 20, 2023 at 06:18:58PM -0700, Josh Poimboeuf wrote: > > Reading the 'spec_rstack_overflow' sysfs file can trigger an unnecessary > > MSR write, and possibly even a (handled) exception if the microcode > > hasn't been updated. > > > > Avoid all that by just checking X86_FEATURE_IBPB_BRTYPE instead, which > > gets set by srso_select_mitigation() if the updated microcode exists. > > > > Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation") > > Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> > > --- > > arch/x86/kernel/cpu/bugs.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c > > index f081d26616ac..bdd3e296f72b 100644 > > --- a/arch/x86/kernel/cpu/bugs.c > > +++ b/arch/x86/kernel/cpu/bugs.c > > @@ -2717,7 +2717,7 @@ static ssize_t srso_show_state(char *buf) > > > > Please put here a comment - something along the lines of: > > "X86_FEATURE_IBPB_BRTYPE gets set as a result of the presence of the > needed microcode so checking that is equivalent." > > so that it is clear why it is ok to check this feature bit.
I could do that, but this check ends up getting replaced by a later patch anyway.
Would you want this comment in srso_select_mitigation()? After the next patch it has:
bool has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE);
Though that seems clear to me already.
-- Josh
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