Re: [PATCH] KVM: Fix kvm_vcpu_map[_readonly]() function prototypes

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

Yosry Ahmed <yosry@kernel.org> writes:

> On Wed, Mar 25, 2026 at 02:15:11AM -0700, Peter Fang wrote:
>> kvm_vcpu_map() and kvm_vcpu_map_readonly() should take a gfn instead of
>> a gpa. This appears to be a result of the original kvm_vcpu_map() being
>> declared with the wrong function prototype in kvm_host.h, even though
>> it was correct in the actual implementation in kvm_main.c.
>> 
>> No actual harm has been done yet as all of the call sites are correctly
>> passing in a gfn. Plus, both gfn_t and gpa_t are typedef'd to u64 so
>> this change shouldn't have any functional impact.
>> 
>> Compile-tested on x86 and ppc, which are the current users of these
>> interfaces.

Mostly a mechanical change. I had looked at ppc call site and looks ok
to me.

>> 
>> Fixes: e45adf665a53 ("KVM: Introduce a new guest mapping API")
>> Cc: KarimAllah Ahmed <karahmed@amazon.de>
>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>> Signed-off-by: Peter Fang <peter.fang@intel.com>
>
> Most callers are converting a GPA to a GFN, I wonder if we should make
> the function take in a GPA instead? But then we'll need to the GPA not
> being aligned to a page boundary (either do gpa_to_gfn() in
> __kvm_vcpu_map() or fail if it's not aligned).
>
> Not sure if that's a net improvement, mostly thinking out loud here.

The suggestion from Yosry and Sean sounds good too. Instead of every
caller of kvm_vcpu_map() doing gpa_to_gfn(), we may as well make
kvm_vcpu_map() accept gpa_t instead and do the gpa_to_gfn() inside
kvm_vcpu_map() in the call to __kvm_vcpu_map(vcpu, gpa_to_gfn(gpa),...),
or within __kvm_vcpu_map() which is fine too, however, the former is a
better approach, IMO.

-ritesh