On Sun, Jan 12, 2025 at 04:50:27PM +0000, Marc Zyngier wrote: > Joey recently reported that some rather basic tests were failing on > NV, and managed to track it down to critical register fields (such as > HCR_EL2.E2H) not having their expect value. > > Further investigation has outlined a couple of critical issues: > > - Evaluating HCR_EL2.E2H must always be done with a sanitising > accessor, no ifs, no buts. Given that KVM assumes a fixed value for > this bit, we cannot leave it to the guest to mess with. > > - Resetting the sysreg file must result in the RESx bits taking > effect. Otherwise, we may end-up making the wrong decision (see > above), and we definitely expose invalid values to the guest. Note > that because we compute the RESx masks very late in the VM setup, we > need to apply these masks at that particular point as well. > > The two patches in this series are enough to fix the current set of > issues, but __vcpu_sys_reg() needs some extra work as it is doing the > wrong thing when used as a lvalue. I'll post a separate series for > that, as the two problems are fairly orthogonal, and this results in a > significant amount of churn. > > All kudos to Joey for patiently tracking that one down. This was > hidden behind a myriad of other issues, and nailing this sucker down > is nothing short of a debugging lesson. Drinks on me next time. > > Unless someone shouts, I'll take this in for 6.14. > Testing using the updated kvm-arm64/nv-next branch: Tested-by: Joey Gouly <joey.gouly@xxxxxxx> Reviewed-by: Joey Gouly <joey.gouly@xxxxxxx> Thanks! Joey > Marc Zyngier (2): > KVM: arm64: nv: Always evaluate HCR_EL2 using sanitising accessors > KVM: arm64: nv: Apply RESx settings to sysreg reset values > > arch/arm64/include/asm/kvm_emulate.h | 36 ++++++++++++---------------- > arch/arm64/include/asm/kvm_nested.h | 2 +- > arch/arm64/kvm/hyp/vhe/sysreg-sr.c | 4 ++-- > arch/arm64/kvm/nested.c | 9 +++++-- > arch/arm64/kvm/sys_regs.c | 5 +++- > 5 files changed, 29 insertions(+), 27 deletions(-) > > -- > 2.39.2 >
