Patch "x86/hyperv: Stop suppressing X86_FEATURE_PCID" has been added to the 4.14-stable tree

[gregkh at linuxfoundation.org]

This is a note to let you know that I've just added the patch titled

    x86/hyperv: Stop suppressing X86_FEATURE_PCID

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-hyperv-stop-suppressing-x86_feature_pcid.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.


>From foo at baz Tue Apr 24 15:29:20 CEST 2018
From: Vitaly Kuznetsov <vkuznets at redhat.com>
Date: Wed, 24 Jan 2018 11:36:29 +0100
Subject: x86/hyperv: Stop suppressing X86_FEATURE_PCID

From: Vitaly Kuznetsov <vkuznets at 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 at redhat.com>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Cc: David Zhang <dazhan at microsoft.com>
Cc: Stephen Hemminger <sthemmin at microsoft.com>
Cc: Haiyang Zhang <haiyangz at microsoft.com>
Cc: "Michael Kelley (EOSG)" <Michael.H.Kelley at microsoft.com>
Cc: Andy Lutomirski <luto at kernel.org>
Cc: devel at linuxdriverproject.org
Cc: "K. Y. Srinivasan" <kys at microsoft.com>
Cc: Aditya Bhandari <adityabh at microsoft.com>
Link: https://lkml.kernel.org/r/20180124103629.29980-1-vkuznets@redhat.com
Signed-off-by: Sasha Levin <alexander.levin at microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 arch/x86/hyperv/mmu.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- a/arch/x86/hyperv/mmu.c
+++ b/arch/x86/hyperv/mmu.c
@@ -137,7 +137,12 @@ static void hyperv_flush_tlb_others(cons
 	}
 
 	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(c
 	}
 
 	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;


Patches currently in stable-queue which might be from vkuznets at redhat.com are

queue-4.14/x86-hyperv-stop-suppressing-x86_feature_pcid.patch
queue-4.14/x86-kvm-vmx-do-not-use-vm-exit-instruction-length-for-fast-mmio-when-running-nested.patch
queue-4.14/x86-hyperv-check-for-required-priviliges-in-hyperv_init.patch