Re: [PATCH 0/5] Fix wrong gfn range of tlb flushing with range

[David Matlack <dmatlack@google.com>]

On Fri, Jun 24, 2022 at 11:36:56AM +0800, Hou Wenlong wrote:
> Commit c3134ce240eed
> ("KVM: Replace old tlb flush function with new one to flush a specified range.")
> replaces old tlb flush function with kvm_flush_remote_tlbs_with_address()
> to do tlb flushing. However, the gfn range of tlb flushing is wrong in
> some cases. E.g., when a spte is dropped, the start gfn of tlb flushing
> should be the gfn of spte not the base gfn of SP which contains the spte.
> So this patchset would fix them and do some cleanups.

One thing that would help prevent future buggy use of
kvm_flush_remote_tlbs_with_address(), and clean up this series, would be to
introduce some helper functions for common operations. In fact, even if
there is only one caller, I still think it would be useful to have helper
functions because it makes it clear the author's intent.

For example, I think the following helpers would be useful in this series:

/* Flush the given page (huge or not) of guest memory. */
static void kvm_flush_remote_tlbs_gfn(struct kvm *kvm, gfn_t gfn, int level)
{
        u64 pages = KVM_PAGES_PER_HPAGE(level);

        kvm_flush_remote_tlbs_with_address(kvm, gfn, pages);
}

/* Flush the range of guest memory mapped by the given SPTE. */
static void kvm_flush_remote_tlbs_sptep(struct kvm *kvm, u64 *sptep)
{
        struct kvm_mmu_page *sp = sptep_to_sp(sptep);
        gfn_t gfn = kvm_mmu_page_get_gfn(sp, spte_index(sptep));

        kvm_flush_remote_tlbs_gfn(kvm, gfn, sp->role.level);
}

/* Flush all memory mapped by the given direct SP. */
static void kvm_flush_remote_tlbs_direct_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
{
        WARN_ON_ONCE(!sp->role.direct);
        kvm_flush_remote_tlbs_gfn(kvm, sp->gfn, sp->role.level + 1);
}

> 
> Hou Wenlong (5):
>   KVM: x86/mmu: Fix wrong gfn range of tlb flushing in
>     validate_direct_spte()
>   KVM: x86/mmu: Fix wrong gfn range of tlb flushing in
>     kvm_set_pte_rmapp()
>   KVM: x86/mmu: Reduce gfn range of tlb flushing in
>     tdp_mmu_map_handle_target_level()
>   KVM: x86/mmu: Fix wrong start gfn of tlb flushing with range
>   KVM: x86/mmu: Use 1 as the size of gfn range for tlb flushing in
>     FNAME(invlpg)()
> 
>  arch/x86/kvm/mmu/mmu.c         | 15 +++++++++------
>  arch/x86/kvm/mmu/paging_tmpl.h |  2 +-
>  arch/x86/kvm/mmu/tdp_mmu.c     |  4 ++--
>  3 files changed, 12 insertions(+), 9 deletions(-)
> 
> --
> 2.31.1
>