linux-kernel - Re: [PATCH V2] RISC-V: KVM: Write hgatp register with valid mode bits

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Message-ID:
 <TY1PPFCDFFFA68ADB818EF448346B258B14F330A@TY1PPFCDFFFA68A.apcprd02.prod.outlook.com>
Date: Tue, 19 Aug 2025 11:47:33 +0800
From: "Nutty.Liu" <nutty.liu@...mail.com>
To: fangyu.yu@...ux.alibaba.com, anup@...infault.org, atish.patra@...ux.dev,
 paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu,
 alex@...ti.fr
Cc: guoren@...ux.alibaba.com, guoren@...nel.org, kvm@...r.kernel.org,
 kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] RISC-V: KVM: Write hgatp register with valid mode bits


On 8/18/2025 1:42 PM, fangyu.yu@...ux.alibaba.com wrote:
> From: Fangyu Yu <fangyu.yu@...ux.alibaba.com>
>
> According to the RISC-V Privileged Architecture Spec, when MODE=Bare
> is selected,software must write zero to the remaining fields of hgatp.
>
> We have detected the valid mode supported by the HW before, So using a
> valid mode to detect how many vmid bits are supported.
>
> Signed-off-by: Fangyu Yu <fangyu.yu@...ux.alibaba.com>
>
> ---
> Changes in v2:
> - Fixed build error since kvm_riscv_gstage_mode() has been modified.
> ---
>   arch/riscv/kvm/vmid.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
Reviewed-by: Nutty Liu <nutty.liu@...mail.com>

Thanks,
Nutty
> diff --git a/arch/riscv/kvm/vmid.c b/arch/riscv/kvm/vmid.c
> index 3b426c800480..5f33625f4070 100644
> --- a/arch/riscv/kvm/vmid.c
> +++ b/arch/riscv/kvm/vmid.c
> @@ -14,6 +14,7 @@
>   #include <linux/smp.h>
>   #include <linux/kvm_host.h>
>   #include <asm/csr.h>
> +#include <asm/kvm_mmu.h>
>   #include <asm/kvm_tlb.h>
>   #include <asm/kvm_vmid.h>
>   
> @@ -28,7 +29,7 @@ void __init kvm_riscv_gstage_vmid_detect(void)
>   
>   	/* Figure-out number of VMID bits in HW */
>   	old = csr_read(CSR_HGATP);
> -	csr_write(CSR_HGATP, old | HGATP_VMID);
> +	csr_write(CSR_HGATP, (kvm_riscv_gstage_mode << HGATP_MODE_SHIFT) | HGATP_VMID);
>   	vmid_bits = csr_read(CSR_HGATP);
>   	vmid_bits = (vmid_bits & HGATP_VMID) >> HGATP_VMID_SHIFT;
>   	vmid_bits = fls_long(vmid_bits);