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Date: Tue, 10 May 2022 14:33:40 +0200 From: Alexander Graf <graf@...zon.com> To: Christophe Leroy <christophe.leroy@...roup.eu>, "kvm@...r.kernel.org" <kvm@...r.kernel.org> CC: "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Paul Mackerras <paulus@...ba.org>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Michael Ellerman <mpe@...erman.id.au>, Matt Evans <matt@...abs.org>, "stable@...r.kernel.org" <stable@...r.kernel.org> Subject: Re: [PATCH v2] KVM: PPC: Book3S PR: Enable MSR_DR for switch_mmu_context() On 10.05.22 13:31, Christophe Leroy wrote: > Le 10/05/2022 à 13:18, Alexander Graf a écrit : >> Commit 863771a28e27 ("powerpc/32s: Convert switch_mmu_context() to C") >> moved the switch_mmu_context() to C. While in principle a good idea, it >> meant that the function now uses the stack. The stack is not accessible >> from real mode though. >> >> So to keep calling the function, let's turn on MSR_DR while we call it. >> That way, all pointer references to the stack are handled virtually. > Is the system ready to handle a DSI in case the stack is not mapped ? A DSI itself will be an interrupt again which will in turn destroy the SPRG that we're saving. Guess I was trying to be too smart :). I'll use Matt's original suggestion and just put it on the stack. >> In addition, make sure to save/restore r12 in an SPRG, as it may get >> clobbered by the C function. >> >> Reported-by: Matt Evans <matt@...abs.org> >> Fixes: 863771a28e27 ("powerpc/32s: Convert switch_mmu_context() to C") > Oops, sorry for that. I didn't realise that there was other callers to > switch_mmu_context() than switch_mm_irqs_off(). No worries, the compiled C version looks a lot nicer than the previous asm one - and it was a good way to identify whether there still are users of KVM on Book3S 32bit out there :) Alex Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879
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