linux-kernel - Re: [PATCH] RISC-V: KVM: Allow to downgrade HGATP mode via SATP mode

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Message-ID: <CAJF2gTTRBFTnu2pA5rh16EWLvF_Wo=+vpZMUK9roDkDPes4Fpg@mail.gmail.com>
Date: Sun, 23 Nov 2025 10:33:19 +0800
From: Guo Ren <guoren@...nel.org>
To: fangyu.yu@...ux.alibaba.com
Cc: anup@...infault.org, atish.patra@...ux.dev, pjw@...nel.org, 
	palmer@...belt.com, aou@...s.berkeley.edu, alex@...ti.fr, 
	ajones@...tanamicro.com, kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] RISC-V: KVM: Allow to downgrade HGATP mode via SATP mode

On Sat, Nov 22, 2025 at 3:50 PM <fangyu.yu@...ux.alibaba.com> wrote:
>
> From: Fangyu Yu <fangyu.yu@...ux.alibaba.com>
>
> Currently, HGATP mode uses the maximum value detected by the hardware
> but often such a wide GPA is unnecessary, just as a host sometimes
> doesn't need sv57.
> It's likely that no additional parameters (like no5lvl and no4lvl) are
> needed, aligning HGATP mode to SATP mode should meet the requirements
> of most scenarios.
Yes, no5/4lvl is not clear about satp or hgatp. So, covering HGPATP is
reasonable.

Acked-by: Guo Ren <guoren@...nel.org>

>
> Signed-off-by: Fangyu Yu <fangyu.yu@...ux.alibaba.com>
> ---
>  arch/riscv/kvm/gstage.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/kvm/gstage.c b/arch/riscv/kvm/gstage.c
> index b67d60d722c2..bff80c80ead3 100644
> --- a/arch/riscv/kvm/gstage.c
> +++ b/arch/riscv/kvm/gstage.c
> @@ -320,7 +320,6 @@ void __init kvm_riscv_gstage_mode_detect(void)
>         csr_write(CSR_HGATP, HGATP_MODE_SV57X4 << HGATP_MODE_SHIFT);
>         if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV57X4) {
>                 kvm_riscv_gstage_mode = HGATP_MODE_SV57X4;
> -               kvm_riscv_gstage_pgd_levels = 5;
>                 goto done;
>         }
>
> @@ -328,7 +327,6 @@ void __init kvm_riscv_gstage_mode_detect(void)
>         csr_write(CSR_HGATP, HGATP_MODE_SV48X4 << HGATP_MODE_SHIFT);
>         if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV48X4) {
>                 kvm_riscv_gstage_mode = HGATP_MODE_SV48X4;
> -               kvm_riscv_gstage_pgd_levels = 4;
>                 goto done;
>         }
>
> @@ -336,7 +334,6 @@ void __init kvm_riscv_gstage_mode_detect(void)
>         csr_write(CSR_HGATP, HGATP_MODE_SV39X4 << HGATP_MODE_SHIFT);
>         if ((csr_read(CSR_HGATP) >> HGATP_MODE_SHIFT) == HGATP_MODE_SV39X4) {
>                 kvm_riscv_gstage_mode = HGATP_MODE_SV39X4;
> -               kvm_riscv_gstage_pgd_levels = 3;
>                 goto done;
>         }
>  #else /* CONFIG_32BIT */
> @@ -354,6 +351,10 @@ void __init kvm_riscv_gstage_mode_detect(void)
>         kvm_riscv_gstage_pgd_levels = 0;
>
>  done:
> +#ifdef CONFIG_64BIT
> +       kvm_riscv_gstage_mode = min(satp_mode >> SATP_MODE_SHIFT, kvm_riscv_gstage_mode);
It's out of the no5/4lvl scope, because we lose (hs-mode)satp=sv39 +
hgatp=sv48x4 combination.

How about re-parsing no5/4lvl parameters?

> +       kvm_riscv_gstage_pgd_levels = kvm_riscv_gstage_mode - HGATP_MODE_SV39X4 + 3;
> +#endif
>         csr_write(CSR_HGATP, 0);
>         kvm_riscv_local_hfence_gvma_all();
>  }
> --
> 2.50.1
>


-- 
Best Regards
 Guo Ren