linux-kernel - Re: [PATCH 15/24] x86/mm: Allow flushing for future ASID switches

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Message-ID: <3ca0bea7-932a-6d91-a9b4-d07045d444f5@linux.intel.com>
Date:   Thu, 30 Nov 2017 07:51:17 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 15/24] x86/mm: Allow flushing for future ASID switches

On 11/30/2017 07:44 AM, Peter Zijlstra wrote:
> On Mon, Nov 27, 2017 at 11:49:14AM +0100, Ingo Molnar wrote:
>> @@ -338,24 +366,23 @@ static inline void __native_flush_tlb_single(unsigned long addr)
>>  
>>  static inline void __flush_tlb_all(void)
>>  {
>> +	if (boot_cpu_has(X86_FEATURE_PGE)) {
>>  		__flush_tlb_global();
>> +	} else {
>>  		__flush_tlb();
>> +		tlb_flush_shared_nonglobals();
> I do however think this one is superfluous; if we do not have PGE we
> also do not have PCID and every CR3 switch flushes everything.

I tried to sprinkle these around at all the sites that did non-global
kernel flushes.  In the case that it's superfluous !KAISER, it's a noop
anyway.  In the (currently unsupported) case that we *do* need it, well,
we need it.

It also makes it a bit more self-documenting that __flush_tlb() does not
flush shared non-globals.