[PATCH v3 1/3] RISC-V: KVM: Treat -EEXIST from G-stage map as success

["Bingyu.Xian" <shanbeeyoo@gmail.com>]

When a concurrent vCPU installs the same G-stage mapping while we are
waiting for mmu_lock, kvm_riscv_gstage_map_page() returns -EEXIST.
This is not an error -- the page is correctly mapped and the faulting
vCPU can simply retry the guest instruction -- but KVM was treating it
as one: printing "Failed to map in G-stage" to dmesg and propagating
-EEXIST all the way to userspace.

Align RISC-V with x86 and arm64, which already swallow -EEXIST in
their respective fault handlers.  This also lets kvm_release_faultin_page()
drop its "ret && ret != -EEXIST" special case: with ret normalized to 0
the regular release path is correct.

Fixes: 9d05c1fee837 ("RISC-V: KVM: Implement stage2 page table programming")
Cc: stable@vger.kernel.org
Assisted-by: YuanSheng: deepseek-v4-pro
Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Bingyu Xian <shanbeeyoo@gmail.com>
---
 arch/riscv/kvm/mmu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index 8a0aa5e0e216..943d8dc72105 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -652,11 +652,13 @@ int kvm_riscv_mmu_map(struct kvm_vcpu *vcpu, struct kvm_memory_slot *memslot,
 						vma_pagesize, true, true, out_map);
 	}
 
-	if (ret)
+	if (ret == -EEXIST)
+		ret = 0;
+	else if (ret)
 		kvm_err("Failed to map in G-stage\n");
 
 out_unlock:
-	kvm_release_faultin_page(kvm, page, ret && ret != -EEXIST, writable);
+	kvm_release_faultin_page(kvm, page, ret, writable);
 	write_unlock(&kvm->mmu_lock);
 	return ret;
 }
-- 
2.54.0