| Message ID | 20211214172812.2894560-2-oupton@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: arm64: Emulate the OS Lock | expand |
Hi Oliver, On Tue, Dec 14, 2021 at 05:28:07PM +0000, Oliver Upton wrote: > Any valid implementation of the architecture should generate an > undefined exception for writes to a read-only register, such as > OSLSR_EL1. Nonetheless, the KVM handler actually implements write-ignore > behavior. > > Align the trap handler for OSLSR_EL1 with hardware behavior. If such a > write ever traps to EL2, inject an undef into the guest and print a > warning. I think this can still be read amibguously, since we don't explicitly state that writes to OSLSR_EL1 should never trap (and the implications of being UNDEFINED are subtle). How about: | Writes to OSLSR_EL1 are UNDEFINED and should never trap from EL1 to EL2, but | the KVM trap handler for OSLSR_EL1 handlees writes via ignore_write(). This | is confusing to readers of the code, but shouldn't have any functional impact. | | For clarity, use write_to_read_only() rather than ignore_write(). If a trap | is unexpectedly taken to EL2 in violation of the architecture, this will | WARN_ONCE() and inject an undef into the guest. With that: Reviewed-by: Mark Rutland <mark.rutland@arm.com> Mark. > Reviewed-by: Reiji Watanabe <reijiw@google.com> > Signed-off-by: Oliver Upton <oupton@google.com> > --- > arch/arm64/kvm/sys_regs.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > index e3ec1a44f94d..11b4212c2036 100644 > --- a/arch/arm64/kvm/sys_regs.c > +++ b/arch/arm64/kvm/sys_regs.c > @@ -292,7 +292,7 @@ static bool trap_oslsr_el1(struct kvm_vcpu *vcpu, > const struct sys_reg_desc *r) > { > if (p->is_write) { > - return ignore_write(vcpu, p); > + return write_to_read_only(vcpu, p, r); > } else { > p->regval = (1 << 3); > return true; > -- > 2.34.1.173.g76aa8bc2d0-goog > > _______________________________________________ > kvmarm mailing list > kvmarm@lists.cs.columbia.edu > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
Hi Mark, On Wed, Dec 15, 2021 at 11:39:58AM +0000, Mark Rutland wrote: > Hi Oliver, > > On Tue, Dec 14, 2021 at 05:28:07PM +0000, Oliver Upton wrote: > > Any valid implementation of the architecture should generate an > > undefined exception for writes to a read-only register, such as > > OSLSR_EL1. Nonetheless, the KVM handler actually implements write-ignore > > behavior. > > > > Align the trap handler for OSLSR_EL1 with hardware behavior. If such a > > write ever traps to EL2, inject an undef into the guest and print a > > warning. > > I think this can still be read amibguously, since we don't explicitly state > that writes to OSLSR_EL1 should never trap (and the implications of being > UNDEFINED are subtle). How about: > > | Writes to OSLSR_EL1 are UNDEFINED and should never trap from EL1 to EL2, but > | the KVM trap handler for OSLSR_EL1 handlees writes via ignore_write(). This > | is confusing to readers of the code, but shouldn't have any functional impact. > | > | For clarity, use write_to_read_only() rather than ignore_write(). If a trap > | is unexpectedly taken to EL2 in violation of the architecture, this will > | WARN_ONCE() and inject an undef into the guest. Agreed, I like your suggested changelog better :-) > With that: > > Reviewed-by: Mark Rutland <mark.rutland@arm.com> Thanks! -- Best, Oliver
On Wed, Dec 15, 2021 at 01:09:28PM +0000, Oliver Upton wrote: > Hi Mark, > > On Wed, Dec 15, 2021 at 11:39:58AM +0000, Mark Rutland wrote: > > Hi Oliver, > > > > On Tue, Dec 14, 2021 at 05:28:07PM +0000, Oliver Upton wrote: > > > Any valid implementation of the architecture should generate an > > > undefined exception for writes to a read-only register, such as > > > OSLSR_EL1. Nonetheless, the KVM handler actually implements write-ignore > > > behavior. > > > > > > Align the trap handler for OSLSR_EL1 with hardware behavior. If such a > > > write ever traps to EL2, inject an undef into the guest and print a > > > warning. > > > > I think this can still be read amibguously, since we don't explicitly state > > that writes to OSLSR_EL1 should never trap (and the implications of being > > UNDEFINED are subtle). How about: > > > > | Writes to OSLSR_EL1 are UNDEFINED and should never trap from EL1 to EL2, but > > | the KVM trap handler for OSLSR_EL1 handlees writes via ignore_write(). This Whoops, with s/handlees/handles/ > > | is confusing to readers of the code, but shouldn't have any functional impact. > > | > > | For clarity, use write_to_read_only() rather than ignore_write(). If a trap > > | is unexpectedly taken to EL2 in violation of the architecture, this will > > | WARN_ONCE() and inject an undef into the guest. > > Agreed, I like your suggested changelog better :-) Cool! Mark. > > > With that: > > > > Reviewed-by: Mark Rutland <mark.rutland@arm.com> > > Thanks! > > -- > Best, > Oliver
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index e3ec1a44f94d..11b4212c2036 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -292,7 +292,7 @@ static bool trap_oslsr_el1(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r) { if (p->is_write) { - return ignore_write(vcpu, p); + return write_to_read_only(vcpu, p, r); } else { p->regval = (1 << 3); return true;