Re: [PATCH v3 17/17] KVM: arm64: Alloc simple_buffer_page using pKVM hyp allocator

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Indiscriminate conversion of `-ENOMEM` into SMCCC top-up requests creates an infinite host kernel retry loop.
--

--- Patch [17]: [PATCH v3 17/17] KVM: arm64: Alloc simple_buffer_page using pKVM hyp allocator ---
commit 1035ec393d7338c6871aee7974ca4f89393be89b
Author: Vincent Donnefort <vdonnefort@google.com>

KVM: arm64: Alloc simple_buffer_page using pKVM hyp allocator

This commit transitions the allocation of the simple_ring_buffer structures
from host-donated memory to the new pKVM hypervisor heap allocator. It
routes hypercalls through pkvm_call_hyp_req() and errno_to_smccc() to
handle heap memory top-up requests automatically during allocation.

> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index 01e7ffc489f5b..a5b740d152be9 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -745,7 +745,7 @@ static void handle___tracing_load(struct kvm_cpu_context *host_ctxt)
>  	DECLARE_REG(unsigned long, desc_hva, host_ctxt, 1);
>  	DECLARE_REG(size_t, desc_size, host_ctxt, 2);
>  
> -	cpu_reg(host_ctxt, 1) = __tracing_load(desc_hva, desc_size);
> +	errno_to_smccc(__tracing_load(desc_hva, desc_size), host_ctxt);

[Severity: High]
Does this create an infinite retry loop in the host if the hypervisor fails
to allocate page tables for the tracing buffer?

If __tracing_load() returns -ENOMEM because hyp_alloc() fails internally
during pkvm_map_private_va_range() (where no top-up is needed and
hyp_alloc_topup_needed() is 0), errno_to_smccc() will unconditionally
intercept the -ENOMEM and create a PKVM_HYP_REQ_HYP_ALLOC request with 0
pages.

The host kernel will successfully process the 0-page top-up in
__pkvm_handle_smccc_req(), which returns 0. Since pkvm_call_hyp_req() loops
on !__ret, this will cause the host to retry the failing hypercall endlessly:

arch/arm64/include/asm/kvm_pkvm.h:pkvm_call_hyp_req() {
    ...
    do {
        ...
        __ret = __pkvm_handle_smccc_req(&__res);
    } while (!__ret);
    ...
}

>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260720171513.1415357-1-vdonnefort@google.com?part=17