From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Wei Liu <wl@xen.org>, Ian Jackson <iwj@xenproject.org>,
xen-devel@lists.xenproject.org,
Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [PATCH 2/2] x86/cpuid: support LFENCE always serializing CPUID bit
Date: Wed, 14 Apr 2021 15:57:22 +0200 [thread overview]
Message-ID: <12301367-e19a-5c89-5751-9937402ac099@suse.com> (raw)
In-Reply-To: <af2cb854-ca3f-22ee-a7b3-8c24fdecfb7e@citrix.com>
On 14.04.2021 15:25, Andrew Cooper wrote:
> On 14/04/2021 14:05, Andrew Cooper wrote:
>> On 14/04/2021 13:57, Jan Beulich wrote:
>>> On 14.04.2021 13:04, Roger Pau Monne wrote:
>>>> @@ -264,6 +265,38 @@ struct cpuid_policy
>>>> };
>>>> uint32_t nc:8, :4, apic_id_size:4, :16;
>>>> uint32_t /* d */:32;
>>>> +
>>>> + uint64_t :64, :64; /* Leaf 0x80000009. */
>>>> + uint64_t :64, :64; /* Leaf 0x8000000a - SVM rev and features. */
>>>> + uint64_t :64, :64; /* Leaf 0x8000000b. */
>>>> + uint64_t :64, :64; /* Leaf 0x8000000c. */
>>>> + uint64_t :64, :64; /* Leaf 0x8000000d. */
>>>> + uint64_t :64, :64; /* Leaf 0x8000000e. */
>>>> + uint64_t :64, :64; /* Leaf 0x8000000f. */
>>>> + uint64_t :64, :64; /* Leaf 0x80000010. */
>>>> + uint64_t :64, :64; /* Leaf 0x80000011. */
>>>> + uint64_t :64, :64; /* Leaf 0x80000012. */
>>>> + uint64_t :64, :64; /* Leaf 0x80000013. */
>>>> + uint64_t :64, :64; /* Leaf 0x80000014. */
>>>> + uint64_t :64, :64; /* Leaf 0x80000015. */
>>>> + uint64_t :64, :64; /* Leaf 0x80000016. */
>>>> + uint64_t :64, :64; /* Leaf 0x80000017. */
>>>> + uint64_t :64, :64; /* Leaf 0x80000018. */
>>>> + uint64_t :64, :64; /* Leaf 0x80000019 - TLB 1GB Identifiers. */
>>>> + uint64_t :64, :64; /* Leaf 0x8000001a - Performance related info. */
>>>> + uint64_t :64, :64; /* Leaf 0x8000001b - IBS feature information. */
>>>> + uint64_t :64, :64; /* Leaf 0x8000001c. */
>>>> + uint64_t :64, :64; /* Leaf 0x8000001d - Cache properties. */
>>>> + uint64_t :64, :64; /* Leaf 0x8000001e - Extd APIC/Core/Node IDs. */
>>>> + uint64_t :64, :64; /* Leaf 0x8000001f - AMD Secure Encryption. */
>>>> + uint64_t :64, :64; /* Leaf 0x80000020 - Platform QoS. */
>>>> +
>>>> + /* Leaf 0x80000021 - Extended Feature 2 */
>>>> + union {
>>>> + uint32_t e21a;
>>>> + struct { DECL_BITFIELD(e21a); };
>>>> + };
>>>> + uint32_t /* b */:32, /* c */:32, /* d */:32;
>>>> };
>>>> } extd;
>>> Due to the effect of this on what guests get to see, I think this
>>> wants to take my "x86/CPUID: shrink max_{,sub}leaf fields according
>>> to actual leaf contents" as a prereq, which in turn may better
>>> remain on top of "x86/CPUID: adjust extended leaves out of range
>>> clearing" (both are neighbors in that over 4 months old series,
>>> fair parts of which could imo go in irrespective of the unsettled
>>> dispute on xvmalloc() - unfortunately I had made that patch 2 of
>>> the series, not expecting it to be blocked for so long, and then
>>> presumably signaling to others that the rest of the series is also
>>> blocked).
>> There is no shrinking to be done in this case. The bit is set across
>> the board on AMD/Hygon hardware, even on older parts.
>>
>> What does need changing however is the logic to trim max_extd_leaf down
>> to what hardware supports, so the bit is visible on Rome/older
>> hardware. I.e. after this change, all VMs should get 0x80000021 by
>> default on AMD hardware.
>>
>> (A curious observation of Milan hardware is that it actually advertises
>> 0x80000023 as max_extd_leaf, and has two leaves of zeros at the end.
>> I've got an open query about this.)
>
> Something like this:
>
> diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
> index 050cd5713e..d9eb2878c5 100644
> --- a/xen/arch/x86/cpuid.c
> +++ b/xen/arch/x86/cpuid.c
> @@ -311,6 +311,7 @@ static void __init calculate_raw_policy(void)
> static void __init calculate_host_policy(void)
> {
> struct cpuid_policy *p = &host_cpuid_policy;
> + unsigned int max_extd_leaf;
>
> *p = raw_cpuid_policy;
>
> @@ -318,7 +319,18 @@ static void __init calculate_host_policy(void)
> min_t(uint32_t, p->basic.max_leaf, ARRAY_SIZE(p->basic.raw) - 1);
> p->feat.max_subleaf =
> min_t(uint32_t, p->feat.max_subleaf, ARRAY_SIZE(p->feat.raw) - 1);
> - p->extd.max_leaf = 0x80000000 | min_t(uint32_t, p->extd.max_leaf &
> 0xffff,
> +
> + max_extd_leaf = p->extd.max_leaf;
> +
> + /*
> + * For AMD/Hygon hardware before Zen3, we modify LFENCE to be dispatch
> + * serialsing. Extend max_extd_leaf beyond what hardware supports, to
> + * include the feature leaf containing this information.
> + */
> + if ( cpu_has_lfence_dispatch )
> + max_extd_leaf = max(max_extd_leaf, 0x80000021);
> +
> + p->extd.max_leaf = 0x80000000 | min_t(uint32_t, max_extd_leaf & 0xffff,
> ARRAY_SIZE(p->extd.raw) - 1);
>
> cpuid_featureset_to_policy(boot_cpu_data.x86_capability, p);
Well, why not set it to ARRAY_SIZE() and then have
x86_cpuid_policy_shrink_max_leaves() (from "x86/CPUID: shrink
max_{,sub}leaf fields according to actual leaf contents") have
a go? It'll recognize the non-zero leaf ... Otherwise, if we
gain a few more such special cases, things are going to get
ugly here.
Jan
next prev parent reply other threads:[~2021-04-14 13:57 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-14 11:04 [PATCH 0/2] x86/amd: LFENCE always serializing CPUID bit Roger Pau Monne
2021-04-14 11:04 ` [PATCH 1/2] x86/amd: split LFENCE dispatch serializing setup logic into helper Roger Pau Monne
2021-04-14 11:11 ` Andrew Cooper
2021-04-14 11:04 ` [PATCH 2/2] x86/cpuid: support LFENCE always serializing CPUID bit Roger Pau Monne
2021-04-14 12:33 ` Andrew Cooper
2021-04-14 12:45 ` Jan Beulich
2021-04-14 12:49 ` Andrew Cooper
2021-04-14 12:57 ` Jan Beulich
2021-04-14 13:05 ` Andrew Cooper
2021-04-14 13:24 ` Jan Beulich
2021-04-14 13:41 ` Andrew Cooper
2021-04-14 13:25 ` Andrew Cooper
2021-04-14 13:57 ` Jan Beulich [this message]
2021-04-15 13:31 ` Roger Pau Monné
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