linux-kernel - Re: [PATCH] RISC-V: KVM: Using user-mode pte within kvm_riscv_gstage

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Message-ID: <CAAhSdy3omyk7YGVHNV5mgR13cON1SxdpqsxGQJsWWE1Hoyw=5A@mail.gmail.com>
Date: Mon, 18 Aug 2025 19:48:39 +0530
From: Anup Patel <anup@...infault.org>
To: fangyu.yu@...ux.alibaba.com
Cc: atish.patra@...ux.dev, paul.walmsley@...ive.com, palmer@...belt.com, 
	aou@...s.berkeley.edu, alex@...ti.fr, guoren@...ux.alibaba.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: Using user-mode pte within kvm_riscv_gstage_ioremap

On Thu, Aug 7, 2025 at 12:37 PM <fangyu.yu@...ux.alibaba.com> wrote:
>
> From: Fangyu Yu <fangyu.yu@...ux.alibaba.com>
>
> Currently we use kvm_riscv_gstage_ioremap to map IMSIC gpa to the spa of
> guest interrupt file within IMSIC.
>
> The PAGE_KERNEL_IO property does not include user mode settings, so when
> accessing the IMSIC address in the virtual machine,  a  guest page fault
> will occur, this is not expected.
>
> According to the RISC-V Privileged Architecture Spec, for G-stage address
> translation, all memory accesses are considered to be user-level accesses
> as though executed in Umode.
>
> Signed-off-by: Fangyu Yu <fangyu.yu@...ux.alibaba.com>

Overall, a good fix. Thanks!

The patch subject and description needs improvements. Also, there is no
Fixes tag which is required for backporting.

I have taken care of the above things at the time of merging this patch.

Queued this patch as fixes for Linux-6.17

Thanks,
Anup

> ---
>  arch/riscv/kvm/mmu.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
> index 1087ea74567b..800064e96ef6 100644
> --- a/arch/riscv/kvm/mmu.c
> +++ b/arch/riscv/kvm/mmu.c
> @@ -351,6 +351,7 @@ int kvm_riscv_gstage_ioremap(struct kvm *kvm, gpa_t gpa,
>         int ret = 0;
>         unsigned long pfn;
>         phys_addr_t addr, end;
> +       pgprot_t prot;
>         struct kvm_mmu_memory_cache pcache = {
>                 .gfp_custom = (in_atomic) ? GFP_ATOMIC | __GFP_ACCOUNT : 0,
>                 .gfp_zero = __GFP_ZERO,
> @@ -359,8 +360,11 @@ int kvm_riscv_gstage_ioremap(struct kvm *kvm, gpa_t gpa,
>         end = (gpa + size + PAGE_SIZE - 1) & PAGE_MASK;
>         pfn = __phys_to_pfn(hpa);
>
> +       prot = pgprot_noncached(PAGE_WRITE);
> +
>         for (addr = gpa; addr < end; addr += PAGE_SIZE) {
> -               pte = pfn_pte(pfn, PAGE_KERNEL_IO);
> +               pte = pfn_pte(pfn, prot);
> +               pte = pte_mkdirty(pte);
>
>                 if (!writable)
>                         pte = pte_wrprotect(pte);
> --
> 2.39.3 (Apple Git-146)
>