[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] x86/AMD: adjust SYSCFG, TOM, etc exposure to deal with running nested
On 19.07.2021 11:18, Julien Grall wrote: > On 13/07/2021 08:22, Jan Beulich wrote: >> In the original change I neglected to consider the case of us running as >> L1 under another Xen. In this case we're not Dom0, so the underlying Xen >> wouldn't permit us access to these MSRs. As an immediate workaround use >> rdmsr_safe(); I don't view this as the final solution though, as the >> original problem the earlier change tried to address also applies when >> running nested. Yet it is then unclear to me how to properly address the >> issue: We shouldn't generally expose the MSR values, but handing back >> zero (or effectively any other static value) doesn't look appropriate >> either. > > IIUC, the unsolved problem is a Linux 3.12 dom0 running on top of the L1 > Xen. The kernel is quite old (and looks to be unsupported), so are we > expecting anyone to build a new stack with a newer Xen and such dom0? > > If the answer is unlikely, then I think it would be fair to keep the > limitation until someone comes up with such setup. I might want to put it differently: If you want to run nested, you shouldn't be using this old a kernel for your Dom0. You saying "looks to be unsupported" is, aiui, a statement from upstream perspective, which distros may have a different view on. >> Fixes: bfcdaae9c210 ("x86/AMD: expose SYSCFG, TOM, TOM2, and IORRs to Dom0") >> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> > > Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx> Thanks. Jan
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