On Wed, Jan 24, 2018 at 4:48 AM, tip-bot for Vitaly Kuznetsov <tipbot@xxxxxxxxx> wrote: > Commit-ID: 04651dd978a8749e59065df14b970a127f219ac2 > Gitweb: https://git.kernel.org/tip/04651dd978a8749e59065df14b970a127f219ac2 > Author: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> > AuthorDate: Wed, 24 Jan 2018 11:36:29 +0100 > Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > CommitDate: Wed, 24 Jan 2018 13:44:57 +0100 > > x86/hyperv: Stop suppressing X86_FEATURE_PCID > > When hypercall-based TLB flush was enabled for Hyper-V guests PCID feature > was deliberately suppressed as a precaution: back then PCID was never > exposed to Hyper-V guests and it wasn't clear what will happen if some day > it becomes available. The day came and PCID/INVPCID features are already > exposed on certain Hyper-V hosts. > > From TLFS (as of 5.0b) it is unclear how TLB flush hypercalls combine with > PCID. In particular the usage of PCID is per-cpu based: the same mm gets > different CR3 values on different CPUs. If the hypercall does exact > matching this will fail. However, this is not the case. David Zhang > explains: > > "In practice, the AddressSpace argument is ignored on any VM that supports > PCIDs. > > Architecturally, the AddressSpace argument must match the CR3 with PCID > bits stripped out (i.e., the low 12 bits of AddressSpace should be 0 in > long mode). The flush hypercalls flush all PCIDs for the specified > AddressSpace." > > With this, PCID can be enabled. So what, exactly, does the flush hypercall do? --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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