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Re: [PATCH v4] x86/nSVM: Validate the L1 IOPM physical address range
- To: Abdelkareem Abdelsaamad <abdelkareem.abdelsaamad@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 18 Aug 2026 11:23:11 +0200
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- Cc: andrew.cooper3@xxxxxxxxxx, roger@xxxxxxxxxxxxxx, jason.andryuk@xxxxxxx, teddy.astie@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 18 Aug 2026 09:23:18 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17.08.2026 18:59, Abdelkareem Abdelsaamad wrote:
> --- a/xen/arch/x86/hvm/svm/nestedsvm.c
> +++ b/xen/arch/x86/hvm/svm/nestedsvm.c
> @@ -282,7 +282,7 @@ static int nsvm_vcpu_hostrestore(struct vcpu *v, struct
> cpu_user_regs *regs)
> return 0;
> }
>
> -static int nsvm_vmrun_permissionmap(struct vcpu *v, bool viopm)
> +static int nsvm_vmrun_permissionmap(struct vcpu *v)
> {
> struct svm_vcpu *arch_svm = &v->arch.hvm.svm;
> struct nestedsvm *svm = &vcpu_nestedsvm(v);
> @@ -294,6 +294,17 @@ static int nsvm_vmrun_permissionmap(struct vcpu *v, bool
> viopm)
> enum hvm_translation_result ret;
> unsigned long *ns_viomap;
> bool ioport_80 = true, ioport_ed = true;
> + /* IOPM is structured as a linear array of 64K+3 bits. */
> + const unsigned long nr_iopm_additional_pages = PFN_DOWN((0x10000 + 8) /
> 8 - 1);
Hm, the expression I did suggest was indeed off by one, yet yours doesn't fit
the comment very well. What's wrong with PFN_DOWN((0x10000 + 3) / 8) or
PFN_DOWN((0xffff + 4) / 8)?
> + gfn_t ns_iopm_end =
> + gfn_add(gaddr_to_gfn(ns_vmcb->_iopm_base_pa),
> nr_iopm_additional_pages);
I'm also inclined to suggest to drop the local variable, as it's used just
here. The overall result would be
/* IOPM is structured as a linear array of 64K+3 bits. */
gfn_t ns_iopm_end = gfn_add(gaddr_to_gfn(ns_vmcb->_iopm_base_pa),
PFN_DOWN((0x10000 + 3) / 8));
which imo is a little easier to follow. Preferably with those adjustments
(happy to carry out while committing, but please confirm):
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Jan
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