Re: [PATCH 15/15] KVM: X86: Always set gpte_is_8_bytes when direct map

Paolo Bonzini
2021-11-18T11:14:59Z

On 11/18/21 12:08, Lai Jiangshan wrote:
> From: Lai Jiangshan <laijs@linux.alibaba.com>
>
> When direct map, gpte_is_8_bytes has no meaning, but it is true for all
> other cases except direct map when nonpaping.
>
> Setting gpte_is_8_bytes to true when nonpaping can ensure that
> !gpte_is_8_bytes means 32-bit gptes for shadow paging.

Then the right thing to do would be to rename it to has_4_byte_gptes and
invert the direction. But as things stand, it's a bit more confusing to
make gpte_is_8_bytes=1 if there are no guest PTEs at all.

Paolo

> Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
> ---
> Documentation/virt/kvm/mmu.rst | 2 +-
> arch/x86/kvm/mmu/mmu.c | 4 ++--
> 2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/virt/kvm/mmu.rst b/Documentation/virt/kvm/mmu.rst
> index f60f5488e121..5d1086602759 100644
> --- a/Documentation/virt/kvm/mmu.rst
> +++ b/Documentation/virt/kvm/mmu.rst
> @@ -179,7 +179,7 @@ Shadow pages contain the following information:
> unpinned it will be destroyed.
> role.gpte_is_8_bytes:
> Reflects the size of the guest PTE for which the page is valid, i.e. '1'
> - if 64-bit gptes are in use, '0' if 32-bit gptes are in use.
> + if direct map or 64-bit gptes are in use, '0' if 32-bit gptes are in use.
> role.efer_nx:
> Contains the value of efer.nx for which the page is valid.
> role.cr0_wp:
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 6948f2d696c3..0c92cbc07320 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2083,7 +2083,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
> role.level = level;
> role.direct = direct;
> role.access = access;
> - if (!direct_mmu && !role.gpte_is_8_bytes) {
> + if (!role.gpte_is_8_bytes) {
> quadrant = gaddr >> (PAGE_SHIFT + (PT64_PT_BITS * level));
> quadrant &= (1 << ((PT32_PT_BITS - PT64_PT_BITS) * level)) - 1;
> role.quadrant = quadrant;
> @@ -4777,7 +4777,7 @@ kvm_calc_shadow_root_page_role_common(struct kvm_vcpu *vcpu,
>
> role.base.smep_andnot_wp = role.ext.cr4_smep && !____is_cr0_wp(regs);
> role.base.smap_andnot_wp = role.ext.cr4_smap && !____is_cr0_wp(regs);
> - role.base.gpte_is_8_bytes = ____is_cr0_pg(regs) && ____is_cr4_pae(regs);
> + role.base.gpte_is_8_bytes = !____is_cr0_pg(regs) || ____is_cr4_pae(regs);
>
> return role;
> }
>