Re: [Qemu-devel] [PATCH] target-i386: add pcid to both Sandy Bridge and Ivy Bridge

[Vincent Bernat <vincent@bernat.im>]

 ❦  8 janvier 2018 19:16 -0200, Eduardo Habkost <ehabkost@redhat.com> :

> One possible way to work around this problem is to declare that
> QEMU 2.12 with KVM will require Linux v3.6 and newer (because we
> need Linux kernel commit ad756a1603c5 "KVM: VMX: Implement
> PCID/INVPCID for guests with EPT").  I have proposed something
> similar to allow us to enable kvm_pv_eoi by default, some time
> ago:
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg486559.html
> ("qemu-doc: Document minimum kernel version for KVM in x86_64").

I don't see a way to probe KVM to know what's supported, so yes. Should
I add a paragraph similar to yours or would your patch be merged soon?
What are the consequences of running a too old kernel? Would KVM just
hide PCID flag?

> Second, we need compatibility entries setting pcid=off on
> PC_COMPAT_2_10 so we don't break compatibility on older
> machine-types.

diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index 6f77eb066587..da5bd8304eb0 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -327,6 +327,14 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
         .driver   = TYPE_X86_CPU,\
         .property = "x-hv-max-vps",\
         .value    = "0x40",\
+    },{\
+        .driver   = "SandyBridge-" TYPE_X86_CPU,\
+        .property = "pcid",\
+        .value    = "off",\
+    },{\
+        .driver   = "IvyBridge-" TYPE_X86_CPU,\
+        .property = "pcid",\
+        .value    = "off",\
     },{\
         .driver   = "i440FX-pcihost",\
         .property = "x-pci-hole64-fix",\

I'll resend a proper patch once the first point is cleared.
-- 
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