On Wed, Jan 25, 2023, Zhi Wang wrote:
> On Thu, 12 Jan 2023 08:31:38 -0800
> isaku.yamahata@xxxxxxxxx wrote:
>
> This refactor patch is quite hacky.
>
> Why not change the purpose of vcpu->arch.mmu_shadow_page.gfp_zero and let the
> callers respect that the initial value of spte can be configurable? It will be
> generic and not TDX-specific, then kvm_init_shadow_page() is not required,
> mmu_topup_shadow_page_cache() can be left un-touched as the refactor can cover
> other architectures.
>
> 1) Let it store the expected nonpresent value and rename it to nonpresent_spte.
I agree that handling this in the common code would be cleaner, but repurposing
gfp_zero gets kludgy because it would require a magic value to say "don't initialize
the data", e.g. x86's mmu_shadowed_info_cache isn't pre-filled.
And supporting a custom 64-bit init value for kmem_cache-backed caches would require
restricting such caches to be a multiple of 8 bytes in size.
How about this? Lightly tested.
From: Sean Christopherson <seanjc@xxxxxxxxxx>
Date: Wed, 25 Jan 2023 16:55:01 +0000
Subject: [PATCH] KVM: Allow page-sized MMU caches to be initialized with
custom 64-bit values
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@xxxxxxxxxx>
---
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 76de36e56cdf..67972db17b55 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 d255964ec331..78f1e49179a7 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -380,12 +380,17 @@ 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)
@@ -400,6 +405,13 @@ 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;
base-commit: 503f0315c97739d3f8e645c500d81757dfbf76be
--
