On Sun, Feb 18, 2024 at 11:47:16PM -0800, Yang Weijiang wrote:
>Tweak the code a bit to facilitate resetting more xstate components in
>the future, e.g., CET's xstate-managed MSRs.
>
>No functional change intended.
Strictly speaking, there is a functional change. in the previous logic, if
either of BNDCSR or BNDREGS state is not supported (kvm_mpx_supported() will
return false), KVM won't reset either of them. Since this gets changed, I vote
to drop 'No functional change ..'
>
>Suggested-by: Chao Gao <chao.gao@xxxxxxxxx>
>Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
>---
> arch/x86/kvm/x86.c | 30 +++++++++++++++++++++++++++---
> 1 file changed, 27 insertions(+), 3 deletions(-)
>
>diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>index 10847e1cc413..5a9c07751c0e 100644
>--- a/arch/x86/kvm/x86.c
>+++ b/arch/x86/kvm/x86.c
>@@ -12217,11 +12217,27 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
> static_branch_dec(&kvm_has_noapic_vcpu);
> }
>
>+#define XSTATE_NEED_RESET_MASK (XFEATURE_MASK_BNDREGS | \
>+ XFEATURE_MASK_BNDCSR)
>+
>+static bool kvm_vcpu_has_xstate(unsigned long xfeature)
kvm_vcpu_has_xstate is a misnomer because it doesn't take a vCPU.
>+{
>+ switch (xfeature) {
>+ case XFEATURE_MASK_BNDREGS:
>+ case XFEATURE_MASK_BNDCSR:
>+ return kvm_cpu_cap_has(X86_FEATURE_MPX);
>+ default:
>+ return false;
>+ }
>+}
>+
> void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> {
> struct kvm_cpuid_entry2 *cpuid_0x1;
> unsigned long old_cr0 = kvm_read_cr0(vcpu);
>+ DECLARE_BITMAP(reset_mask, 64);
> unsigned long new_cr0;
>+ unsigned int i;
>
> /*
> * Several of the "set" flows, e.g. ->set_cr0(), read other registers
>@@ -12274,7 +12290,12 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> kvm_async_pf_hash_reset(vcpu);
> vcpu->arch.apf.halted = false;
>
>- if (vcpu->arch.guest_fpu.fpstate && kvm_mpx_supported()) {
>+ bitmap_from_u64(reset_mask, (kvm_caps.supported_xcr0 |
>+ kvm_caps.supported_xss) &
>+ XSTATE_NEED_RESET_MASK);
>+
>+ if (vcpu->arch.guest_fpu.fpstate &&
>+ !bitmap_empty(reset_mask, XFEATURE_MAX)) {
> struct fpstate *fpstate = vcpu->arch.guest_fpu.fpstate;
>
> /*
>@@ -12284,8 +12305,11 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> if (init_event)
> kvm_put_guest_fpu(vcpu);
>
>- fpstate_clear_xstate_component(fpstate, XFEATURE_BNDREGS);
>- fpstate_clear_xstate_component(fpstate, XFEATURE_BNDCSR);
>+ for_each_set_bit(i, reset_mask, XFEATURE_MAX) {
>+ if (!kvm_vcpu_has_xstate(i))
>+ continue;
The kvm_vcpu_has_xstate() check is superfluous because @i is derived from
kvm_caps.supported_xcr0/xss, which already guarantees that all unsupported
xfeatures are filtered out.
I recommend dropping this check. w/ this change,
Reviewed-by: Chao Gao <chao.gao@xxxxxxxxx>
>+ fpstate_clear_xstate_component(fpstate, i);
>+ }
>
> if (init_event)
> kvm_load_guest_fpu(vcpu);
>--
>2.43.0
>
