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    SubjectRe: [PATCH v13 030/113] KVM: Allow page-sized MMU caches to be initialized with custom 64-bit values
    On Sun, 12 Mar 2023 10:55:54 -0700
    isaku.yamahata@intel.com wrote:

    > From: Sean Christopherson <seanjc@google.com>
    >
    > Add support to MMU caches for initializing a page with a custom 64-bit
    > value, e.g. to pre-fill an entire page table with non-zero PTE values.
    > The functionality will be used by x86 to support Intel's TDX, which needs
    > to set bit 63 in all non-present PTEs in order to prevent !PRESENT page
    > faults from getting reflected into the guest (Intel's EPT Violation #VE
    > architecture made the less than brilliant decision of having the per-PTE
    > behavior be opt-out instead of opt-in).
    >
    > Signed-off-by: Sean Christopherson <seanjc@google.com>

    Your Sighned-off-by is required as well.

    > ---
    > include/linux/kvm_types.h | 1 +
    > virt/kvm/kvm_main.c | 16 ++++++++++++++--
    > 2 files changed, 15 insertions(+), 2 deletions(-)
    >
    > diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
    > index 2728d49bbdf6..7c2b9332b7c5 100644
    > --- a/include/linux/kvm_types.h
    > +++ b/include/linux/kvm_types.h
    > @@ -94,6 +94,7 @@ struct kvm_mmu_memory_cache {
    > int nobjs;
    > gfp_t gfp_zero;
    > gfp_t gfp_custom;
    > + u64 init_value;
    > struct kmem_cache *kmem_cache;
    > int capacity;
    > void **objects;
    > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
    > index f8495e27d210..87400796df6e 100644
    > --- a/virt/kvm/kvm_main.c
    > +++ b/virt/kvm/kvm_main.c
    > @@ -381,12 +381,17 @@ static void kvm_flush_shadow_all(struct kvm *kvm)
    > static inline void *mmu_memory_cache_alloc_obj(struct kvm_mmu_memory_cache *mc,
    > gfp_t gfp_flags)
    > {
    > + void *page;
    > +
    > gfp_flags |= mc->gfp_zero;
    >
    > if (mc->kmem_cache)
    > return kmem_cache_alloc(mc->kmem_cache, gfp_flags);
    > - else
    > - return (void *)__get_free_page(gfp_flags);
    > +
    > + page = (void *)__get_free_page(gfp_flags);
    > + if (page && mc->init_value)
    > + memset64(page, mc->init_value, PAGE_SIZE / sizeof(mc->init_value));
    > + return page;
    > }
    >
    > int __kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int capacity, int min)
    > @@ -401,6 +406,13 @@ int __kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int capacity,
    > if (WARN_ON_ONCE(!capacity))
    > return -EIO;
    >
    > + /*
    > + * Custom init values can be used only for page allocations,
    > + * and obviously conflict with __GFP_ZERO.
    > + */
    > + if (WARN_ON_ONCE(mc->init_value && (mc->kmem_cache || mc->gfp_zero)))
    > + return -EIO;
    > +
    > mc->objects = kvmalloc_array(sizeof(void *), capacity, gfp);
    > if (!mc->objects)
    > return -ENOMEM;

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