Messages in this thread | | | Date | Wed, 9 Aug 2023 15:36:19 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 11/17] x86/cpu: Remove all SRSO interface nonsense |
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On Wed, Aug 09, 2023 at 02:10:42PM +0100, Andrew.Cooper3@citrix.com wrote: > On 09/08/2023 8:12 am, Peter Zijlstra wrote: > > Now that retbleed can do all that the srso knob did, and without the > > dubious interactions with retbleed selections, remove it. > > > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > > --- > > arch/x86/kernel/cpu/bugs.c | 188 ++------------------------------------------- > > drivers/base/cpu.c | 8 - > > include/linux/cpu.h | 2 > > 3 files changed, 10 insertions(+), 188 deletions(-) > > Not all of this can go, because ... > > > --- a/arch/x86/kernel/cpu/bugs.c > > +++ b/arch/x86/kernel/cpu/bugs.c > > ... > > -static void __init srso_select_mitigation(void) > > -{ > > - bool has_microcode; > > - > > - if (!boot_cpu_has_bug(X86_BUG_SRSO) || cpu_mitigations_off()) > > - goto pred_cmd; > > - > > - /* > > - * The first check is for the kernel running as a guest in order > > - * for guests to verify whether IBPB is a viable mitigation. > > - */ > > - has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE) || cpu_has_ibpb_brtype_microcode(); > > - if (!has_microcode) { > > - pr_warn("IBPB-extending microcode not applied!\n"); > > - pr_warn(SRSO_NOTICE); > > - } else { > > - /* > > - * Enable the synthetic (even if in a real CPUID leaf) > > - * flags for guests. > > - */ > > - setup_force_cpu_cap(X86_FEATURE_IBPB_BRTYPE); > > - setup_force_cpu_cap(X86_FEATURE_SBPB); > > ... these (minus the virt bug caused by probing for microcode behaviour > even when virtualised, and the enumeration bug caused by ignoring > synthesis if host mitigations are off) are necessary for KVM. > > https://www.amd.com/content/dam/amd/en/documents/corporate/cr/speculative-return-stack-overflow-whitepaper.pdf > > and here's one I prepared earlier > https://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=2280b0ee2aed6e0fd4af3fa31bf99bc04d038bfe > > but these bits need to get into guests for the guests to be able to > figure out what to do.
Patch 6 adds these feature bits to retbleed_select_mitigation().
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