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

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Message-Id: <20250819012558.88733-1-fangyu.yu@linux.alibaba.com>
Date: Tue, 19 Aug 2025 09:25:58 +0800
From: fangyu.yu@...ux.alibaba.com
To: anup@...infault.org
Cc: alex@...ti.fr,
	aou@...s.berkeley.edu,
	atish.patra@...ux.dev,
	fangyu.yu@...ux.alibaba.com,
	guoren@...ux.alibaba.com,
	kvm-riscv@...ts.infradead.org,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	palmer@...belt.com,
	paul.walmsley@...ive.com
Subject: Re: [PATCH] RISC-V: KVM: Using user-mode pte within kvm_riscv_gstage_ioremap

>>
>> 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
>

Thanks for your review.
I will send a v2 patch to fix these comments.

Thanks,
fangyu

>> ---
>>  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)
>>