From: "H. Peter Anvin" <hpa@zytor.com>
To: Andrew Cooper <Andrew.Cooper3@citrix.com>,
Peter Zijlstra <peterz@infradead.org>, Xin Li <xin3.li@intel.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"seanjc@google.com" <seanjc@google.com>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"ravi.v.shankar@intel.com" <ravi.v.shankar@intel.com>
Subject: Re: [RFC PATCH 22/32] x86/fred: FRED initialization code
Date: Fri, 23 Dec 2022 11:37:07 -0800 [thread overview]
Message-ID: <9D8B895D-0728-4451-BD22-B8EC78F90BEB@zytor.com> (raw)
In-Reply-To: <16972e64-7d7b-ad8c-f8dc-6dcab69e629e@citrix.com>
On December 20, 2022 1:55:31 AM PST, Andrew Cooper <Andrew.Cooper3@citrix.com> wrote:
>On 20/12/2022 9:45 am, Peter Zijlstra wrote:
>> On Mon, Dec 19, 2022 at 10:36:48PM -0800, Xin Li wrote:
>>
>>> + wrmsrl(MSR_IA32_FRED_STKLVLS,
>>> + FRED_STKLVL(X86_TRAP_DB, 1) |
>>> + FRED_STKLVL(X86_TRAP_NMI, 2) |
>>> + FRED_STKLVL(X86_TRAP_MC, 2) |
>>> + FRED_STKLVL(X86_TRAP_DF, 3));
>>> +
>>> + /* The FRED equivalents to IST stacks... */
>>> + wrmsrl(MSR_IA32_FRED_RSP1, __this_cpu_ist_top_va(DB));
>>> + wrmsrl(MSR_IA32_FRED_RSP2, __this_cpu_ist_top_va(NMI));
>>> + wrmsrl(MSR_IA32_FRED_RSP3, __this_cpu_ist_top_va(DF));
>> Not quite.. IIRC fred only switches to another stack when the level of
>> the exception is higher. Specifically, if we trigger #DB while inside
>> #NMI we will not switch to the #DB stack (since 1 < 2).
>
>There needs to be a new stack for #DF, and just possibly one for #MC.
>NMI and #DB do not need separate stacks under FRED.
>
>> Now, as mentioned elsewhere, it all nests a lot saner, but stack
>> exhaustion is still a thing, given the above, what happens when a #DB
>> hits an #NMI which tickles a #VE or something?
>>
>> I don't think we've increased the exception stack size, but perhaps we
>> should for FRED?
>
>Not sure if it matters too much - it doesn't seem usefully different to
>IDT delivery. #DB shouldn't get too deep, and NMI gets properly
>inhibited now.
>
>~Andrew
>
I still don't think you want to take #DB or – especially – NMI on the task stack while in the kernel. In fact, the plan is to get rid of the software irqstack handling, too, but at tglx's request that will be a later changeset (correctness first, then optimization.)
next prev parent reply other threads:[~2022-12-23 19:37 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-20 6:36 [RFC PATCH 00/32] x86: enable FRED for x86-64 Xin Li
2022-12-20 6:36 ` [RFC PATCH 01/32] x86/traps: let common_interrupt() handle IRQ_MOVE_CLEANUP_VECTOR Xin Li
2022-12-20 6:36 ` [RFC PATCH 02/32] x86/traps: add a system interrupt table for system interrupt dispatch Xin Li
2022-12-20 6:36 ` [RFC PATCH 03/32] x86/traps: add install_system_interrupt_handler() Xin Li
2022-12-20 6:36 ` [RFC PATCH 04/32] x86/traps: add external_interrupt() to dispatch external interrupts Xin Li
2022-12-20 6:36 ` [RFC PATCH 05/32] x86/traps: add exc_raise_irq() for VMX IRQ reinjection Xin Li
2023-01-09 18:20 ` Li, Xin3
2022-12-20 6:36 ` [RFC PATCH 06/32] x86/cpufeature: add the cpu feature bit for FRED Xin Li
2022-12-20 6:36 ` [RFC PATCH 07/32] x86/opcode: add ERETU, ERETS instructions to x86-opcode-map Xin Li
2022-12-20 6:36 ` [RFC PATCH 08/32] x86/objtool: teach objtool about ERETU and ERETS Xin Li
2022-12-20 6:36 ` [RFC PATCH 09/32] x86/cpu: add X86_CR4_FRED macro Xin Li
2022-12-20 6:36 ` [RFC PATCH 10/32] x86/fred: add Kconfig option for FRED (CONFIG_X86_FRED) Xin Li
2022-12-20 6:36 ` [RFC PATCH 11/32] x86/fred: if CONFIG_X86_FRED is disabled, disable FRED support Xin Li
2022-12-20 6:36 ` [RFC PATCH 12/32] x86/cpu: add MSR numbers for FRED configuration Xin Li
2022-12-20 6:36 ` [RFC PATCH 13/32] x86/fred: header file for event types Xin Li
2022-12-20 6:36 ` [RFC PATCH 14/32] x86/fred: header file with FRED definitions Xin Li
2022-12-20 8:56 ` Peter Zijlstra
2022-12-21 2:58 ` Li, Xin3
2022-12-22 13:03 ` Peter Zijlstra
2022-12-23 19:34 ` H. Peter Anvin
2022-12-20 6:36 ` [RFC PATCH 15/32] x86/fred: make unions for the cs and ss fields in struct pt_regs Xin Li
2022-12-20 6:36 ` [RFC PATCH 16/32] x86/fred: reserve space for the FRED stack frame Xin Li
2022-12-20 6:36 ` [RFC PATCH 17/32] x86/fred: add a page fault entry stub for FRED Xin Li
2022-12-20 6:36 ` [RFC PATCH 18/32] x86/fred: add a debug " Xin Li
2022-12-20 9:15 ` Peter Zijlstra
2022-12-20 6:36 ` [RFC PATCH 19/32] x86/fred: add a NMI " Xin Li
2022-12-20 6:36 ` [RFC PATCH 20/32] x86/fred: add a machine check " Xin Li
2022-12-20 6:36 ` [RFC PATCH 21/32] x86/fred: FRED entry/exit and dispatch code Xin Li
2022-12-20 9:35 ` Peter Zijlstra
2022-12-21 2:56 ` Li, Xin3
2022-12-22 13:08 ` Peter Zijlstra
2022-12-20 6:36 ` [RFC PATCH 22/32] x86/fred: FRED initialization code Xin Li
2022-12-20 9:45 ` Peter Zijlstra
2022-12-20 9:55 ` Andrew Cooper
2022-12-20 10:02 ` Peter Zijlstra
2022-12-21 5:28 ` Li, Xin3
2022-12-21 5:44 ` H. Peter Anvin
2022-12-22 13:09 ` Peter Zijlstra
2022-12-23 19:30 ` H. Peter Anvin
2022-12-23 19:37 ` H. Peter Anvin [this message]
2022-12-20 6:36 ` [RFC PATCH 23/32] x86/fred: update MSR_IA32_FRED_RSP0 during task switch Xin Li
2022-12-20 9:48 ` Peter Zijlstra
2022-12-20 18:47 ` Li, Xin3
2022-12-23 19:42 ` H. Peter Anvin
2022-12-24 3:02 ` Li, Xin3
2022-12-20 6:36 ` [RFC PATCH 24/32] x86/fred: let ret_from_fork() jmp to fred_exit_user when FRED is enabled Xin Li
2022-12-20 6:36 ` [RFC PATCH 25/32] x86/fred: disallow the swapgs instruction " Xin Li
2022-12-20 6:36 ` [RFC PATCH 26/32] x86/fred: no ESPFIX needed " Xin Li
2022-12-20 6:36 ` [RFC PATCH 27/32] x86/fred: allow single-step trap and NMI when starting a new thread Xin Li
2022-12-20 6:36 ` [RFC PATCH 28/32] x86/fred: fixup fault on ERETU by jumping to fred_entrypoint_user Xin Li
2022-12-20 6:36 ` [RFC PATCH 29/32] x86/ia32: do not modify the DPL bits for a null selector Xin Li
2022-12-20 6:36 ` [RFC PATCH 30/32] x86/fred: allow FRED systems to use interrupt vectors 0x10-0x1f Xin Li
2022-12-20 6:36 ` [RFC PATCH 31/32] x86/fred: allow dynamic stack frame size Xin Li
2022-12-20 6:36 ` [RFC PATCH 32/32] x86/fred: disable FRED by default in its early stage Xin Li
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