On Tue, Nov 03, 2020 at 11:18:19AM +0000, Dave Martin wrote:

On Mon, Nov 02, 2020 at 07:50:35PM +0100, Andrew Jones wrote:

...

ID registers are RAZ until they've been allocated a purpose, but that doesn't mean they should be removed from the KVM_GET_REG_LIST list. So far we only have one register, SYS_ID_AA64ZFR0_EL1, that is hidden from userspace when its function is not present. Removing the userspace visibility checks is enough to reexpose it, as it already behaves as RAZ when the function is not present.

Pleae state what the patch does. (The subject line serves as a summary of that, but the commit message should make sense without it.)

I don't like "This patch ..." type of sentences in the commit message, but unless you have a better suggestion, then I'd just add a sentence like

"This patch ensures we still expose sysreg '3, 0, 0, 4, 4' (ID_AA64ZFR0_EL1) to userspace as RAZ when SVE is not implemented."

Also, how exactly !vcpu_has_sve() causes ID_AA64ZFR0_EL1 to behave as RAZ with this change? (I'm not saying it doesn't, but the code is not trivial to follow...)

guest_id_aa64zfr0_el1() returns zero for the register when !vcpu_has_sve(), and all the accessors (userspace and guest) build on it.

I'm not sure how helpful it would be to add that sentence to the commit message though.

...

Fixes: 73433762fcae ("KVM: arm64/sve: System register context switch and access support") Cc: stable@vger.kernel.org # v5.2+ Reported-by: 张东旭 xu910121@sina.com Signed-off-by: Andrew Jones drjones@redhat.com

---

arch/arm64/kvm/sys_regs.c | 18 +----------------- 1 file changed, 1 insertion(+), 17 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index fb12d3ef423a..6ff0c15531ca 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -1195,16 +1195,6 @@ static unsigned int sve_visibility(const struct kvm_vcpu *vcpu, return REG_HIDDEN_USER | REG_HIDDEN_GUEST; } -/* Visibility overrides for SVE-specific ID registers */ -static unsigned int sve_id_visibility(const struct kvm_vcpu *vcpu,

• 		      const struct sys_reg_desc *rd)
  

-{

• if (vcpu_has_sve(vcpu))

• return 0;
  

• return REG_HIDDEN_USER;

In light of this change, I think that REG_HIDDEN_GUEST and REG_HIDDEN_USER are always either both set or both clear. Given the discussion on this issue, I'm thinking it probably doesn't even make sense for these to be independent (?)

If REG_HIDDEN_USER is really redundant, I suggest stripping it out and simplifying the code appropriately.

(In effect, I think your RAZ flag will do correctly what REG_HIDDEN_USER was trying to achieve.)

We could consolidate REG_HIDDEN_GUEST and REG_HIDDEN_USER into REG_HIDDEN, which ZCR_EL1 and ptrauth registers will still use.

...

-}

/* Generate the emulated ID_AA64ZFR0_EL1 value exposed to the guest */ static u64 guest_id_aa64zfr0_el1(const struct kvm_vcpu *vcpu) { @@ -1231,9 +1221,6 @@ static int get_id_aa64zfr0_el1(struct kvm_vcpu *vcpu, { u64 val;

• if (WARN_ON(!vcpu_has_sve(vcpu)))

• return -ENOENT;
  

• val = guest_id_aa64zfr0_el1(vcpu); return reg_to_user(uaddr, &val, reg->id);

} @@ -1246,9 +1233,6 @@ static int set_id_aa64zfr0_el1(struct kvm_vcpu *vcpu, int err; u64 val;

• if (WARN_ON(!vcpu_has_sve(vcpu)))

• return -ENOENT;
  

• err = reg_from_user(&val, uaddr, id); if (err) return err;

@@ -1518,7 +1502,7 @@ static const struct sys_reg_desc sys_reg_descs[] = { ID_SANITISED(ID_AA64PFR1_EL1), ID_UNALLOCATED(4,2), ID_UNALLOCATED(4,3),

• { SYS_DESC(SYS_ID_AA64ZFR0_EL1), access_id_aa64zfr0_el1, .get_user = get_id_aa64zfr0_el1, .set_user = set_id_aa64zfr0_el1, .visibility = sve_id_visibility },

• { SYS_DESC(SYS_ID_AA64ZFR0_EL1), access_id_aa64zfr0_el1, .get_user = get_id_aa64zfr0_el1, .set_user = set_id_aa64zfr0_el1, }, ID_UNALLOCATED(4,5), ID_UNALLOCATED(4,6), ID_UNALLOCATED(4,7),

Otherwise looks reasonable.

Thanks, drew