linux-kernel - Re: [PATCH] RISC-V: KVM: Avoid re-acquiring memslot in kvm_riscv_gstage

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Message-ID: <20250611-352bef23df9a4ec55fe5cb68@orel>
Date: Wed, 11 Jun 2025 13:29:01 +0200
From: Andrew Jones <ajones@...tanamicro.com>
To: zhouquan@...as.ac.cn
Cc: anup@...infault.org, atishp@...shpatra.org, paul.walmsley@...ive.com, 
	palmer@...belt.com, linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org
Subject: Re: [PATCH] RISC-V: KVM: Avoid re-acquiring memslot in
 kvm_riscv_gstage_map()

On Wed, Jun 11, 2025 at 05:51:40PM +0800, zhouquan@...as.ac.cn wrote:
> From: Quan Zhou <zhouquan@...as.ac.cn>
> 
> The caller has already passed in the memslot, and there are
> two instances `{kvm_faultin_pfn/mark_page_dirty}` of retrieving
> the memslot again in `kvm_riscv_gstage_map`, we can replace them
> with `{__kvm_faultin_pfn/mark_page_dirty_in_slot}`.
> 
> Signed-off-by: Quan Zhou <zhouquan@...as.ac.cn>
> ---
>  arch/riscv/kvm/mmu.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
> index 1087ea74567b..f9059dac3ba3 100644
> --- a/arch/riscv/kvm/mmu.c
> +++ b/arch/riscv/kvm/mmu.c
> @@ -648,7 +648,8 @@ int kvm_riscv_gstage_map(struct kvm_vcpu *vcpu,
>  		return -EFAULT;
>  	}
>  
> -	hfn = kvm_faultin_pfn(vcpu, gfn, is_write, &writable, &page);
> +	hfn = __kvm_faultin_pfn(memslot, gfn, is_write ? FOLL_WRITE : 0,
> +				&writable, &page);

I think introducing another function with the following diff would be
better than duplicating the is_write to foll translation.

Thanks,
drew

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 291d49b9bf05..6c80ad5c7e89 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1288,12 +1288,20 @@ kvm_pfn_t __kvm_faultin_pfn(const struct kvm_memory_slot *slot, gfn_t gfn,
                            unsigned int foll, bool *writable,
                            struct page **refcounted_page);

+static inline kvm_pfn_t kvm_faultin_pfn_in_slot(const struct kvm_memory_slot *slot,
+                                               gfn_t gfn,
+                                               unsigned int foll, bool *writable,
+                                               struct page **refcounted_page)
+{
+       return __kvm_faultin_pfn(slot, gfn, write ? FOLL_WRITE : 0, writable, refcounted_page);
+}
+
 static inline kvm_pfn_t kvm_faultin_pfn(struct kvm_vcpu *vcpu, gfn_t gfn,
                                        bool write, bool *writable,
                                        struct page **refcounted_page)
 {
-       return __kvm_faultin_pfn(kvm_vcpu_gfn_to_memslot(vcpu, gfn), gfn,
-                                write ? FOLL_WRITE : 0, writable, refcounted_page);
+       return kvm_faultin_pfn_in_slot(kvm_vcpu_gfn_to_memslot(vcpu, gfn), gfn,
+                                      write, writable, refcounted_page);
 }

>  	if (hfn == KVM_PFN_ERR_HWPOISON) {
>  		send_sig_mceerr(BUS_MCEERR_AR, (void __user *)hva,
>  				vma_pageshift, current);
> @@ -670,7 +671,7 @@ int kvm_riscv_gstage_map(struct kvm_vcpu *vcpu,
>  		goto out_unlock;
>  
>  	if (writable) {
> -		mark_page_dirty(kvm, gfn);
> +		mark_page_dirty_in_slot(kvm, memslot, gfn);
>  		ret = gstage_map_page(kvm, pcache, gpa, hfn << PAGE_SHIFT,
>  				      vma_pagesize, false, true);
>  	} else {
> -- 
> 2.34.1
>