linux-kernel - Re: [PATCH v4 2/4] RISC-V: KVM: Detect and expose supported HGATP G-stage modes

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Message-Id: <DG4PS6NRRUC1.1FL8WBJVEEM4D@oss.qualcomm.com>
Date: Mon, 02 Feb 2026 19:14:21 +0000
From: Radim Krčmář
 <radim.krcmar@....qualcomm.com>
To: <fangyu.yu@...ux.alibaba.com>, <pbonzini@...hat.com>, <corbet@....net>,
        <anup@...infault.org>, <atish.patra@...ux.dev>, <pjw@...nel.org>,
        <palmer@...belt.com>, <aou@...s.berkeley.edu>, <alex@...ti.fr>
Cc: <guoren@...nel.org>, <ajones@...tanamicro.com>, <rkrcmar@...tanamicro.com>,
        <andrew.jones@....qualcomm.com>, <linux-doc@...r.kernel.org>,
        <kvm@...r.kernel.org>, <kvm-riscv@...ts.infradead.org>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/4] RISC-V: KVM: Detect and expose supported HGATP
 G-stage modes

2026-02-02T22:07:14+08:00, <fangyu.yu@...ux.alibaba.com>:
> From: Fangyu Yu <fangyu.yu@...ux.alibaba.com>
>
> Extend kvm_riscv_gstage_mode_detect() to probe all HGATP.MODE values
> supported by the host and record them in a bitmask. Keep tracking the
> maximum supported G-stage page table level for existing internal users.
>
> Also provide lightweight helpers to retrieve the supported-mode bitmask
> and validate a requested HGATP.MODE against it.
>
> Signed-off-by: Fangyu Yu <fangyu.yu@...ux.alibaba.com>
> ---
> diff --git a/arch/riscv/include/asm/kvm_gstage.h b/arch/riscv/include/asm/kvm_gstage.h
> @@ -75,4 +76,40 @@ void kvm_riscv_gstage_wp_range(struct kvm_gstage *gstage, gpa_t start, gpa_t end
> +enum kvm_riscv_hgatp_mode_bit {
> +	HGATP_MODE_SV39X4_BIT = 0,
> +	HGATP_MODE_SV48X4_BIT = 1,
> +	HGATP_MODE_SV57X4_BIT = 2,

I think it's a bit awkward to pass 9 when selecting the hgatp mode, but
then look for bit 0 when detecting it...
Why not to use the RVI defined values for this UABI as well?

There are only 16 possible hgatp.mode values, so we're fine storing them
in a bitmap even on RV32.

Thanks.