Messages in this thread | | | Date | Thu, 30 Apr 2015 15:30:04 -0400 | From | Boris Ostrovsky <> | Subject | Re: [PATCH] hypervisor/x86/xen: Unset X86_BUG_SYSRET_SS_ATTRS on Xen PV guests |
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On 04/30/2015 03:17 PM, Andy Lutomirski wrote: > On Thu, Apr 30, 2015 at 12:08 PM, Boris Ostrovsky > <boris.ostrovsky@oracle.com> wrote: >> Commit 61f01dd941ba ("x86_64, asm: Work around AMD SYSRET SS descriptor >> attribute issue") makes AMD processors set SS to __KERNEL_DS in >> __switch_to() to deal with cases when SS is NULL. >> >> This breaks Xen PV guests who do not want to load SS with__KERNEL_DS. >> >> Since the problem that the commit is trying to address would have to be >> fixed in the hypervisor (if it in fact exists under Xen) there is no >> reason to set X86_BUG_SYSRET_SS_ATTRS flag for PV VPCUs here. >> > Seems reasonable. > > Have you run the test case on a Xen PV guest on AMD? It's possible > that Xen is affected, since the old accidental workaround that we > deleted was in the vdso and probably would have worked on Xen.
Is there a specific test that would trigger this bug? I booted/suspended/resumed a bunch of various guest types on both AMD and Intel but not much more than that. What is the commit that you deleted?
I doubt that a change in the guest could suddenly start triggering this issue but I will take a look at hypervisor code.
-boris
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