From: Vitaly Kuznetsov vkuznets@redhat.com
[ Upstream commit 617ab45c9a8900e64a78b43696c02598b8cad68b ]
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.
Signed-off-by: Vitaly Kuznetsov vkuznets@redhat.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: David Zhang dazhan@microsoft.com Cc: Stephen Hemminger sthemmin@microsoft.com Cc: Haiyang Zhang haiyangz@microsoft.com Cc: "Michael Kelley (EOSG)" Michael.H.Kelley@microsoft.com Cc: Andy Lutomirski luto@kernel.org Cc: devel@linuxdriverproject.org Cc: "K. Y. Srinivasan" kys@microsoft.com Cc: Aditya Bhandari adityabh@microsoft.com Link: https://lkml.kernel.org/r/20180124103629.29980-1-vkuznets@redhat.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- arch/x86/hyperv/mmu.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c index 9cc9e1c1e2db..56c9ebac946f 100644 --- a/arch/x86/hyperv/mmu.c +++ b/arch/x86/hyperv/mmu.c @@ -137,7 +137,12 @@ static void hyperv_flush_tlb_others(const struct cpumask *cpus, }
if (info->mm) { + /* + * AddressSpace argument must match the CR3 with PCID bits + * stripped out. + */ flush->address_space = virt_to_phys(info->mm->pgd); + flush->address_space &= CR3_ADDR_MASK; flush->flags = 0; } else { flush->address_space = 0; @@ -219,7 +224,12 @@ static void hyperv_flush_tlb_others_ex(const struct cpumask *cpus, }
if (info->mm) { + /* + * AddressSpace argument must match the CR3 with PCID bits + * stripped out. + */ flush->address_space = virt_to_phys(info->mm->pgd); + flush->address_space &= CR3_ADDR_MASK; flush->flags = 0; } else { flush->address_space = 0; @@ -278,8 +288,6 @@ void hyperv_setup_mmu_ops(void) if (!(ms_hyperv.hints & HV_X64_REMOTE_TLB_FLUSH_RECOMMENDED)) return;
- setup_clear_cpu_cap(X86_FEATURE_PCID); - if (!(ms_hyperv.hints & HV_X64_EX_PROCESSOR_MASKS_RECOMMENDED)) { pr_info("Using hypercall for remote TLB flush\n"); pv_mmu_ops.flush_tlb_others = hyperv_flush_tlb_others;