[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] hap_invlpg() vs INVLPGA
On 29/01/16 14:24, Jan Beulich wrote: > Christoph, > > in commit dd6de3ab99 ("Implement Nested-on-Nested") you added > code to hap_invlpg() supposedly emulating INVLPGA. I've been > stumbling across this a number of times in the past, not being able > to make the connection between (a) VMX/EPT and INVLPGA and > (b) SVM's INVLPGA intercept and this function. When you boot Windows 7 as L1 guest and XP-Mode as L2 guest then L2 guest uses INVLPG instruction to invalidate a page and L1 guest handles this via using INVLPGA instruction. The INVLPG intercept flushes the nested hap p2m which is effectively a TLB flush to the L1 guest. Then this intercept is injected into L1 guest. The INVLPGA instruction enforces a new ASID. If the nested hap p2m is NULL then p2m_flush() should effectively be a noop but it may not crash the guest. What I don't remember is if Windows 7 must be 32bit or 64bit to reproduce this. Christoph > I'm asking in the context of a reported crash resulting from the > nv_p2m field being NULL during emulation of an INVLPG instruction > in a guest with nesting enabled but - afaict - not actually used. Of > course I could submit a patch adding a NULL check here, but I'd > like to understand what this code is for, and hence whether the > better fix wouldn't be to get rid of it. > > Jan Amazon Development Center Germany GmbH Berlin - Dresden - Aachen main office: Krausenstr. 38, 10117 Berlin Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger Ust-ID: DE289237879 Eingetragen am Amtsgericht Charlottenburg HRB 149173 B _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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