linux-kernel - Re: [PATCH] x86/speculation/l1tf: fix off-by-one error when warning that system has too much RAM

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Message-ID: <73314d45-85bc-2a7d-a839-9c9ab4260592@gmail.com>
Date:   Tue, 28 Aug 2018 19:04:03 -0700
From:   Christopher Snowhill <kode54@...il.com>
To:     Andre Tomt <andre@...t.net>, Andi Kleen <ak@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Michal Hocko <mhocko@...nel.org>, stable@...r.kernel.org,
        George Anchev <studio@...hev.net>
Subject: Re: [PATCH] x86/speculation/l1tf: fix off-by-one error when warning
 that system has too much RAM



On 08/23/2018 07:22 PM, Andre Tomt wrote:
> On 23. aug. 2018 17:44, Andi Kleen wrote:
>> On Thu, Aug 23, 2018 at 03:44:18PM +0200, Vlastimil Babka wrote:
>>> Two users have reported [1] that they have an "extremely unlikely"
>>> system
>>> with more than MAX_PA/2 memory and L1TF mitigation is not effective.
>>> In fact
>>> it's a CPU with 36bits phys limit (64GB) and 32GB memory, but due to
>>> holes
>>> in the e820 map, the main region is almost 500MB over the 32GB limit:
>>
>> Ah I see it's a client part with very large DIMMs and someone being
>> very brave and using that much memory without ECC.
>
> FYI; It is also happening on Xeon E3v2 (Ivy Bridge generation) w/ 32GB
> of ECC RAM here, a low-end server part that officially supports up to
> 32GB.
>

Indeed, I must be "very brave" to not have chucked this CPU and
motherboard and RAM in the bin, and bought a new board, Xeon CPU, and
ECC RAM. Maybe I'll consider that in the future, when I again have
$1000+ to buy new kit. Which will probably be never, at this rate.

>> [    0.000000] microcode: microcode updated early to revision 0x20,
>> date = 2018-04-10
>> [    0.029728] L1TF: System has more than MAX_PA/2 memory. L1TF
>> mitigation not effective.
>> [    1.063155] microcode: sig=0x306a9, pf=0x2, revision=0x20
>
>
>> processor    : 7
>> vendor_id    : GenuineIntel
>> cpu family    : 6
>> model        : 58
>> model name    : Intel(R) Xeon(R) CPU E3-1230 V2 @ 3.30GHz
>> stepping    : 9
>> microcode    : 0x20
>> cpu MHz        : 3500.044
>> cache size    : 8192 KB
>> physical id    : 0
>> siblings    : 8
>> core id        : 3
>> cpu cores    : 4
>> apicid        : 7
>> initial apicid    : 7
>> fpu        : yes
>> fpu_exception    : yes
>> cpuid level    : 13
>> wp        : yes
>> flags        : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
>> mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe
>> syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl
>> xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor
>> ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic
>> popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm
>> cpuid_fault epb pti ssbd ibrs ibpb stibp tpr_shadow vnmi flexpriority
>> ept vpid fsgsbase smep erms xsaveopt dtherm ida arat pln pts flush_l1d
>> bugs        : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf
>> bogomips    : 6602.15
>> clflush size    : 64
>> cache_alignment    : 64
>> address sizes    : 36 bits physical, 48 bits virtual
>> power management:
>
>


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