From: "Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@linux.intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@kernel.org>, Peter H Anvin <hpa@zytor.com>,
Dave Hansen <dave.hansen@intel.com>,
Tony Luck <tony.luck@intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Andi Kleen <ak@linux.intel.com>,
Kirill Shutemov <kirill.shutemov@linux.intel.com>,
Sean Christopherson <seanjc@google.com>,
Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 08/12] x86/tdx: Add HLT support for TDX guest
Date: Tue, 24 Aug 2021 10:35:33 -0700 [thread overview]
Message-ID: <a3f0731c-c27f-8c20-19f9-0aa609d36288@linux.intel.com> (raw)
In-Reply-To: <YSUaAQPiBUqubBHM@zn.tnic>
On 8/24/21 9:10 AM, Borislav Petkov wrote:
> On Wed, Aug 04, 2021 at 11:13:25AM -0700, Kuppuswamy Sathyanarayanan wrote:
>> @@ -240,6 +243,32 @@ SYM_FUNC_START(__tdx_hypercall)
>>
>> movl $TDVMCALL_EXPOSE_REGS_MASK, %ecx
>>
>> + /*
>> + * For the idle loop STI needs to be called directly before
>> + * the TDCALL that enters idle (EXIT_REASON_HLT case). STI
>> + * enables interrupts only one instruction later. If there
>> + * are any instructions between the STI and the TDCALL for
>> + * HLT then an interrupt could happen in that time, but the
>> + * code would go back to sleep afterwards, which can cause
>> + * longer delays.
>
> <-- newline in the comment here for better readability.
Ok. I will add it in next version.
>
>> There leads to significant difference in
>
> "There leads..." ?
Will fix this in next version. "This leads"
>
>> + * network performance benchmarks. So add a special case for
>> + * EXIT_REASON_HLT to trigger sti before TDCALL. But this
>> + * change is not required for all HLT cases. So use R15
>> + * register value to identify the case which needs sti. So,
>
> s/sti/STI/g
will fix this in next version.
>
>> + * if R11 is EXIT_REASON_HLT and R15 is 1, then call sti
>> + * before TDCALL instruction. Note that R15 register is not
>> + * required by TDCALL ABI when triggering the hypercall for
>> + * EXIT_REASON_HLT case. So use it in software to select the
>> + * sti case.
>> + */
>> + cmpl $EXIT_REASON_HLT, %r11d
>> + jne skip_sti
>> + cmpl $1, %r15d
>> + jne skip_sti
>> + /* Set R15 register to 0, it is unused in EXIT_REASON_HLT case */
>> + xor %r15, %r15
>> + sti
>> +skip_sti:
>> tdcall
>
> ...
>
>> +static __cpuidle void tdg_safe_halt(void)
>> +{
>> + u64 ret;
>> +
>> + /*
>> + * Enable interrupts next to the TDVMCALL to avoid
>> + * performance degradation.
>
> That comment needs some more love to say exactly what the problem is.
It is a bug in this submission. After adding STI fix, this local_irq_enable()
had to be removed. Somehow I have missed to do it. I will fix this
in next version.
>
>> + */
>> + local_irq_enable();
>> +
>> + /* IRQ is enabled, So set R12 as 0 */
>> + ret = _tdx_hypercall(EXIT_REASON_HLT, 0, 0, 0, 1, NULL);
>> +
>> + /* It should never fail */
>> + BUG_ON(ret);
>> +}
>
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer
next prev parent reply other threads:[~2021-08-24 17:46 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-04 18:13 [PATCH v5 00/12] Add TDX Guest Support (Initial support) Kuppuswamy Sathyanarayanan
2021-08-04 18:13 ` [PATCH v5 01/12] x86/paravirt: Move halt paravirt calls under CONFIG_PARAVIRT Kuppuswamy Sathyanarayanan
2021-08-12 7:18 ` Borislav Petkov
2021-08-12 17:17 ` Kuppuswamy, Sathyanarayanan
2021-08-17 12:50 ` Juergen Gross
2021-08-17 13:16 ` Kuppuswamy, Sathyanarayanan
2021-08-17 13:28 ` Juergen Gross
2021-08-17 13:39 ` Kuppuswamy, Sathyanarayanan
2021-08-17 13:47 ` Juergen Gross
2021-08-17 13:50 ` Kuppuswamy, Sathyanarayanan
2021-08-04 18:13 ` [PATCH v5 02/12] x86/tdx: Introduce INTEL_TDX_GUEST config option Kuppuswamy Sathyanarayanan
2021-08-04 18:13 ` [PATCH v5 03/12] x86/cpufeatures: Add TDX Guest CPU feature Kuppuswamy Sathyanarayanan
2021-08-12 7:39 ` Borislav Petkov
2021-08-04 18:13 ` [PATCH v5 04/12] x86/tdx: Add protected guest support for TDX guest Kuppuswamy Sathyanarayanan
2021-08-04 21:59 ` Sean Christopherson
2021-08-04 22:03 ` Dave Hansen
2021-08-04 22:26 ` Kuppuswamy, Sathyanarayanan
2021-08-04 22:42 ` Sean Christopherson
2021-08-04 23:00 ` Kuppuswamy, Sathyanarayanan
2021-08-12 7:53 ` Borislav Petkov
2021-08-12 17:18 ` Kuppuswamy, Sathyanarayanan
2021-08-20 14:28 ` Borislav Petkov
2021-08-20 16:42 ` Kuppuswamy, Sathyanarayanan
2021-08-20 16:59 ` Borislav Petkov
2021-08-20 17:11 ` Kuppuswamy, Sathyanarayanan
2021-08-04 18:13 ` [PATCH v5 05/12] x86/tdx: Add __tdx_module_call() and __tdx_hypercall() helper functions Kuppuswamy Sathyanarayanan
2021-08-20 15:16 ` Borislav Petkov
2021-08-04 18:13 ` [PATCH v5 06/12] x86/tdx: Get TD execution environment information via TDINFO Kuppuswamy Sathyanarayanan
2021-08-04 22:38 ` Sean Christopherson
2021-08-20 17:13 ` Borislav Petkov
2021-08-20 17:31 ` Kuppuswamy, Sathyanarayanan
2021-08-20 17:35 ` Borislav Petkov
2021-08-20 18:29 ` Kuppuswamy, Sathyanarayanan
2021-08-20 18:58 ` Andi Kleen
2021-08-20 19:01 ` Kuppuswamy, Sathyanarayanan
2021-08-04 18:13 ` [PATCH v5 07/12] x86/traps: Add #VE support for TDX guest Kuppuswamy Sathyanarayanan
2021-08-24 10:17 ` Borislav Petkov
2021-08-24 17:32 ` Kuppuswamy, Sathyanarayanan
2021-08-24 17:36 ` Dave Hansen
2021-08-24 17:46 ` Borislav Petkov
2021-09-02 15:24 ` Kuppuswamy, Sathyanarayanan
2021-09-03 10:17 ` Borislav Petkov
2021-08-04 18:13 ` [PATCH v5 08/12] x86/tdx: Add HLT " Kuppuswamy Sathyanarayanan
2021-08-24 16:10 ` Borislav Petkov
2021-08-24 17:06 ` Sean Christopherson
2021-08-24 17:25 ` Andi Kleen
2021-08-24 17:27 ` Borislav Petkov
2021-08-24 17:47 ` Sean Christopherson
2021-08-24 17:50 ` Borislav Petkov
2021-08-31 20:49 ` Kuppuswamy, Sathyanarayanan
2021-09-01 7:42 ` Borislav Petkov
2021-08-24 18:18 ` Kuppuswamy, Sathyanarayanan
2021-08-24 18:28 ` Andi Kleen
2021-08-24 17:35 ` Kuppuswamy, Sathyanarayanan [this message]
2021-08-24 17:48 ` Borislav Petkov
2021-08-04 18:13 ` [PATCH v5 09/12] x86/tdx: Wire up KVM hypercalls Kuppuswamy Sathyanarayanan
2021-08-24 16:34 ` Borislav Petkov
2021-08-24 18:11 ` Kuppuswamy, Sathyanarayanan
2021-08-24 18:29 ` Borislav Petkov
2021-08-24 19:11 ` Kuppuswamy, Sathyanarayanan
2021-08-24 19:39 ` Borislav Petkov
2021-08-04 18:13 ` [PATCH v5 10/12] x86/tdx: Add MSR support for TDX guest Kuppuswamy Sathyanarayanan
2021-08-24 16:55 ` Borislav Petkov
2021-08-24 18:12 ` Kuppuswamy, Sathyanarayanan
2021-08-04 18:13 ` [PATCH v5 11/12] x86/tdx: Don't write CSTAR MSR on Intel Kuppuswamy Sathyanarayanan
2021-08-04 18:31 ` Sean Christopherson
2021-08-04 21:03 ` Kuppuswamy, Sathyanarayanan
2021-08-04 21:44 ` Sean Christopherson
2021-08-04 21:48 ` Dave Hansen
2021-08-04 22:23 ` Kuppuswamy, Sathyanarayanan
2021-08-04 18:13 ` [PATCH v5 12/12] x86/tdx: Handle CPUID via #VE Kuppuswamy Sathyanarayanan
2021-08-24 17:48 ` Borislav Petkov
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