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KVM: x86/mmu: Snapshot shadow_phys_bits when kvm.ko is loaded

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Snapshot shadow_phys_bits when kvm.ko is loaded, not when a vendor module
is loaded, to guard against usage of shadow_phys_bits before it is
initialized.  The computation isn't vendor specific in any way, i.e. there
there is no reason to wait to snapshot the value until a vendor module is
loaded, nor is there any reason to recompute the value every time a vendor
module is loaded.

Opportunistically convert it from "read mostly" to "read-only after init".

Link: https://lore.kernel.org/r/20240423221521.2923759-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2024-04-23 15:15:20 -07:00
parent 52c47f5897
commit c043eaaa6b
2 changed files with 4 additions and 4 deletions
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2
arch/x86/kvm/mmu.h
View File

@ -61,7 +61,7 @@ static __always_inline u64 rsvd_bits(int s, int e)
* The number of non-reserved physical address bits irrespective of features
* that repurpose legal bits, e.g. MKTME.
*/
extern u8 __read_mostly shadow_phys_bits;
extern u8 __ro_after_init shadow_phys_bits;
static inline gfn_t kvm_mmu_max_gfn(void)
{

6
arch/x86/kvm/mmu/spte.c
View File

@ -43,7 +43,7 @@ u64 __read_mostly shadow_acc_track_mask;
u64 __read_mostly shadow_nonpresent_or_rsvd_mask;
u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask;
u8 __read_mostly shadow_phys_bits;
u8 __ro_after_init shadow_phys_bits;
void __init kvm_mmu_spte_module_init(void)
{
@ -55,6 +55,8 @@ void __init kvm_mmu_spte_module_init(void)
* will change when the vendor module is (re)loaded.
*/
allow_mmio_caching = enable_mmio_caching;
shadow_phys_bits = kvm_get_shadow_phys_bits();
}
static u64 generation_mmio_spte_mask(u64 gen)
@ -441,8 +443,6 @@ void kvm_mmu_reset_all_pte_masks(void)
u8 low_phys_bits;
u64 mask;
shadow_phys_bits = kvm_get_shadow_phys_bits();
/*
* If the CPU has 46 or less physical address bits, then set an
* appropriate mask to guard against L1TF attacks. Otherwise, it is