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93390c0a1b
Currently, a guest kernel sees the true CPU feature registers (ID_*_EL1) when it reads them using MRS instructions. This means that the guest may observe features that are present in the hardware but the host doesn't understand or doesn't provide support for. A guest may legimitately try to use such a feature as per the architecture, but use of the feature may trap instead of working normally, triggering undef injection into the guest. This is not a problem for the host, but the guest may go wrong when running on newer hardware than the host knows about. This patch hides from guest VMs any AArch64-specific CPU features that the host doesn't support, by exposing to the guest the sanitised versions of the registers computed by the cpufeatures framework, instead of the true hardware registers. To achieve this, HCR_EL2.TID3 is now set for AArch64 guests, and emulation code is added to KVM to report the sanitised versions of the affected registers in response to MRS and register reads from userspace. The affected registers are removed from invariant_sys_regs[] (since the invariant_sys_regs handling is no longer quite correct for them) and added to sys_reg_desgs[], with appropriate access(), get_user() and set_user() methods. No runtime vcpu storage is allocated for the registers: instead, they are read on demand from the cpufeatures framework. This may need modification in the future if there is a need for userspace to customise the features visible to the guest. Attempts by userspace to write the registers are handled similarly to the current invariant_sys_regs handling: writes are permitted, but only if they don't attempt to change the value. This is sufficient to support VM snapshot/restore from userspace. Because of the additional registers, restoring a VM on an older kernel may not work unless userspace knows how to handle the extra VM registers exposed to the KVM user ABI by this patch. Under the principle of least damage, this patch makes no attempt to handle any of the other registers currently in invariant_sys_regs[], or to emulate registers for AArch32: however, these could be handled in a similar way in future, as necessary. Signed-off-by: Dave Martin <Dave.Martin@arm.com> Reviewed-by: Marc Zyngier <marc.zyngier@arm.com> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Christoffer Dall <christoffer.dall@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> |
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| .. | ||
| debug-sr.c | ||
| entry.S | ||
| fpsimd.S | ||
| hyp-entry.S | ||
| Makefile | ||
| s2-setup.c | ||
| switch.c | ||
| sysreg-sr.c | ||
| tlb.c | ||