[PATCH v4 08/10] RISC-V: KVM: avoid EBUSY when writing the same isa_ext val

Daniel Henrique Barboza
2023-08-03T16:33:40Z

riscv_vcpu_set_isa_ext_single() will prevent any write of isa_ext regs
if the vcpu already started spinning.

But if there's no extension state (enabled/disabled) made by the
userspace, there's no need to -EBUSY out - we can treat the operation as
a no-op.

zicbom/zicboz_block_size, ISA config reg and mvendorid/march/mimpid
already works in a more permissive manner w.r.t userspace writes being a
no-op, so let's do the same with isa_ext writes.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
---
arch/riscv/kvm/vcpu_onereg.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/riscv/kvm/vcpu_onereg.c b/arch/riscv/kvm/vcpu_onereg.c
index 81cb6b2784db..989ea32dbcbe 100644
--- a/arch/riscv/kvm/vcpu_onereg.c
+++ b/arch/riscv/kvm/vcpu_onereg.c
@@ -482,6 +482,9 @@ static int riscv_vcpu_set_isa_ext_single(struct kvm_vcpu *vcpu,
if (!__riscv_isa_extension_available(NULL, host_isa_ext))
return -ENOENT;

+ if (reg_val == test_bit(host_isa_ext, vcpu->arch.isa))
+ return 0;
+
if (!vcpu->arch.ran_atleast_once) {
/*
* All multi-letter extension and a few single letter