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Date: Wed, 3 Jun 2020 16:23:25 +0200 From: Joerg Roedel <joro@...tes.org> To: Sean Christopherson <sean.j.christopherson@...el.com> Cc: x86@...nel.org, hpa@...or.com, Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, Peter Zijlstra <peterz@...radead.org>, Thomas Hellstrom <thellstrom@...are.com>, Jiri Slaby <jslaby@...e.cz>, Dan Williams <dan.j.williams@...el.com>, Tom Lendacky <thomas.lendacky@....com>, Juergen Gross <jgross@...e.com>, Kees Cook <keescook@...omium.org>, David Rientjes <rientjes@...gle.com>, Cfir Cohen <cfir@...gle.com>, Erdem Aktas <erdemaktas@...gle.com>, Masami Hiramatsu <mhiramat@...nel.org>, Mike Stunes <mstunes@...are.com>, Joerg Roedel <jroedel@...e.de>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org Subject: Re: [PATCH v3 25/75] x86/sev-es: Add support for handling IOIO exceptions Hi Jean, On Tue, May 19, 2020 at 11:20:55PM -0700, Sean Christopherson wrote: > On Tue, Apr 28, 2020 at 05:16:35PM +0200, Joerg Roedel wrote: > > + /* > > + * For the string variants with rep prefix the amount of in/out > > + * operations per #VC exception is limited so that the kernel > > + * has a chance to take interrupts an re-schedule while the > > + * instruction is emulated. > > Doesn't this also suppress single-step #DBs? Yes it does. > > > + */ > > + io_bytes = (exit_info_1 >> 4) & 0x7; > > + ghcb_count = sizeof(ghcb->shared_buffer) / io_bytes; > > + > > + op_count = (exit_info_1 & IOIO_REP) ? regs->cx : 1; > > + exit_info_2 = min(op_count, ghcb_count); > > + exit_bytes = exit_info_2 * io_bytes; > > + > > + es_base = insn_get_seg_base(ctxt->regs, INAT_SEG_REG_ES); > > + > > + if (!(exit_info_1 & IOIO_TYPE_IN)) { > > + ret = vc_insn_string_read(ctxt, > > + (void *)(es_base + regs->si), > > SEV(-ES) is 64-bit only, why bother with the es_base charade? User-space can also cause IOIO #VC exceptions, and user-space can be 32-bit legacy code with segments, so es_base has to be taken into account. > > > + ghcb->shared_buffer, io_bytes, > > + exit_info_2, df); > > df handling is busted, it's aways non-zero. Same goes for the SI/DI > adjustments below. Right, this is fixed now. > Batching the memory accesses and I/O accesses separately is technically > wrong, e.g. a #DB on a memory access will result in bogus data being shown > in the debugger. In practice it seems unlikely to matter, but I'm curious > as to why string I/O is supported in the first place. I didn't think there > was that much string I/O in the kernel? True, #DBs won't be correct anymore. Currently debugging is not supported in SEV-ES guests anyway, but if it is supported the #DB exception would happen in the #VC handler and not on the original instruction. Regards, Joerg
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