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Date: Thu, 14 Oct 2021 09:24:43 +0800 From: Xiaoyao Li <xiaoyao.li@...el.com> To: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuwamy@...ux.intel.com>, Sean Christopherson <seanjc@...gle.com>, Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>, xiaoyao.li@...el.com Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>, David Hildenbrand <david@...hat.com>, Andrea Arcangeli <aarcange@...hat.com>, Josh Poimboeuf <jpoimboe@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Dave Hansen <dave.hansen@...el.com>, Tony Luck <tony.luck@...el.com>, Dan Williams <dan.j.williams@...el.com>, Andi Kleen <ak@...ux.intel.com>, Kirill Shutemov <kirill.shutemov@...ux.intel.com>, Kuppuswamy Sathyanarayanan <knsathya@...nel.org>, linux-kernel@...r.kernel.org Subject: Re: [PATCH v7 6/6] x86/split_lock: Fix the split lock #AC handling when running as guest On 10/14/2021 5:32 AM, Sathyanarayanan Kuppuswamy wrote: > + Xiaoyao > > On 10/13/21 1:30 PM, Sean Christopherson wrote: >> On Tue, Oct 05, 2021, Kuppuswamy Sathyanarayanan wrote: >>> From: Xiaoyao Li <xiaoyao.li@...el.com> >>> >>> If running as guest and hypervisor enables >>> MSR_TEST_CTRL.SPLIT_LOCK_DETECT during its running, it can get split >>> lock #AC even though sld_state is sld_off. >> That's a hypervisor bug, no? The hypervisor should never inject a >> fault that >> the guest cannot reasonably expect. What if hypervisor doesn't intercept #AC and host enables SPLIT_LOCK_DETECT during guest running? That's exactly the case TDX is facing. (BTW, this patch is not complete that no matter what state sld_state is, it should always treat it as fatal even sld_warn because sld_warn doesn't guarantee SPLIT_LOCK_DETECT is available) Sathya, we need to drop this one. Andi has anther one to disable split lock detection for SPR. That's a better direction. >>> For kernel mode #AC, it always dies("split lock"), no more action >>> needed. >>> >>> For user mode #AC, it should treat sld_off (default state when feature >>> is not available) as fatal as well. >>> >>> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com> >>> Signed-off-by: Kuppuswamy Sathyanarayanan >>> <sathyanarayanan.kuppuswamy@...ux.intel.com> >>> --- >>> arch/x86/kernel/cpu/intel.c | 7 ++++++- >>> 1 file changed, 6 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c >>> index 01d7935feaed..47f0bc95ce2a 100644 >>> --- a/arch/x86/kernel/cpu/intel.c >>> +++ b/arch/x86/kernel/cpu/intel.c >>> @@ -1190,7 +1190,12 @@ static void bus_lock_init(void) >>> bool handle_user_split_lock(struct pt_regs *regs, long error_code) >>> { >>> - if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal) >>> + /* >>> + * In virtualization environment, it can get split lock #AC even >>> when >>> + * sld_off but hypervisor enables it. >>> + * Thus only handles when sld_warn explicitly. >>> + */ >>> + if ((regs->flags & X86_EFLAGS_AC) || sld_state != sld_warn) >>> return false; >>> split_lock_warn(regs->ip); >>> return true; >>> -- >>> 2.25.1 >>>
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