Excerpts from Ram Pai's message of July 16, 2020 6:32 pm: > An instruction accessing a mmio address, generates a HDSI fault. This fault > is > appropriately handled by the Hypervisor. However in the case of secureVMs, > the > fault is delivered to the ultravisor.
Why not a ucall if you're paraultravizing it anyway? > > Unfortunately the Ultravisor has no correct-way to fetch the faulting > instruction. The PEF architecture does not allow Ultravisor to enable MMU > translation. Walking the two level page table to read the instruction can race > with other vcpus modifying the SVM's process scoped page table. > > This problem can be correctly solved with some help from the kernel. > > Capture the faulting instruction in SPRG0 register, before executing the > faulting instruction. This enables the ultravisor to easily procure the > faulting instruction and emulate it. > > Signed-off-by: Ram Pai <[email protected]> > --- > arch/powerpc/include/asm/io.h | 85 > ++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 75 insertions(+), 10 deletions(-) > > diff --git a/arch/powerpc/include/asm/io.h b/arch/powerpc/include/asm/io.h > index 635969b..7ef663d 100644 > --- a/arch/powerpc/include/asm/io.h > +++ b/arch/powerpc/include/asm/io.h > @@ -35,6 +35,7 @@ > #include <asm/mmu.h> > #include <asm/ppc_asm.h> > #include <asm/pgtable.h> > +#include <asm/svm.h> > > #define SIO_CONFIG_RA 0x398 > #define SIO_CONFIG_RD 0x399 > @@ -105,34 +106,98 @@ > static inline u##size name(const volatile u##size __iomem *addr) \ > { \ > u##size ret; \ > - __asm__ __volatile__("sync;"#insn" %0,%y1;twi 0,%0,0;isync" \ > - : "=r" (ret) : "Z" (*addr) : "memory"); \ > + if (is_secure_guest()) { \ > + __asm__ __volatile__("mfsprg0 %3;" \ > + "lnia %2;" \ > + "ld %2,12(%2);" \ > + "mtsprg0 %2;" \ > + "sync;" \ > + #insn" %0,%y1;" \ > + "twi 0,%0,0;" \ > + "isync;" \ > + "mtsprg0 %3" \ We prefer to use mtspr in new code, and the nia offset should be calculated with a label I think "(1f - .)(%2)" should work. SPRG usage is documented in arch/powerpc/include/asm/reg.h if this goes past RFC stage. Looks like SPRG0 probably could be used for this. Thanks, Nick
