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kvm: arm64: Dynamic configuration of VTTBR mask
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On arm64 VTTBR_EL2:BADDR holds the base address for the stage2
translation table. The Arm ARM mandates that the bits BADDR[x-1:0]
should be 0, where 'x' is defined for a given IPA Size and the
number of levels for a translation granule size. It is defined
using some magical constants. This patch is a reverse engineered
implementation to calculate the 'x' at runtime for a given ipa and
number of page table levels. See patch for more details.

Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Christoffer Dall <cdall@kernel.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
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Suzuki K Poulose authored and Marc Zyngier committed Oct 1, 2018
1 parent 61fa5a8 commit 5955833
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Showing 2 changed files with 88 additions and 10 deletions.
73 changes: 64 additions & 9 deletions arch/arm64/include/asm/kvm_arm.h
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Original file line number Diff line number Diff line change
Expand Up @@ -123,7 +123,6 @@
#define VTCR_EL2_SL0_MASK (3 << VTCR_EL2_SL0_SHIFT)
#define VTCR_EL2_SL0_LVL1 (1 << VTCR_EL2_SL0_SHIFT)
#define VTCR_EL2_T0SZ_MASK 0x3f
#define VTCR_EL2_T0SZ_40B 24
#define VTCR_EL2_VS_SHIFT 19
#define VTCR_EL2_VS_8BIT (0 << VTCR_EL2_VS_SHIFT)
#define VTCR_EL2_VS_16BIT (1 << VTCR_EL2_VS_SHIFT)
Expand All @@ -140,11 +139,8 @@
* Note that when using 4K pages, we concatenate two first level page tables
* together. With 16K pages, we concatenate 16 first level page tables.
*
* The magic numbers used for VTTBR_X in this patch can be found in Tables
* D4-23 and D4-25 in ARM DDI 0487A.b.
*/

#define VTCR_EL2_T0SZ_IPA VTCR_EL2_T0SZ_40B
#define VTCR_EL2_COMMON_BITS (VTCR_EL2_SH0_INNER | VTCR_EL2_ORGN0_WBWA | \
VTCR_EL2_IRGN0_WBWA | VTCR_EL2_RES1)

Expand All @@ -155,29 +151,88 @@
* 2 level page tables (SL = 1)
*/
#define VTCR_EL2_TGRAN_FLAGS (VTCR_EL2_TG0_64K | VTCR_EL2_SL0_LVL1)
#define VTTBR_X_TGRAN_MAGIC 38
#elif defined(CONFIG_ARM64_16K_PAGES)
/*
* Stage2 translation configuration:
* 16kB pages (TG0 = 2)
* 2 level page tables (SL = 1)
*/
#define VTCR_EL2_TGRAN_FLAGS (VTCR_EL2_TG0_16K | VTCR_EL2_SL0_LVL1)
#define VTTBR_X_TGRAN_MAGIC 42
#else /* 4K */
/*
* Stage2 translation configuration:
* 4kB pages (TG0 = 0)
* 3 level page tables (SL = 1)
*/
#define VTCR_EL2_TGRAN_FLAGS (VTCR_EL2_TG0_4K | VTCR_EL2_SL0_LVL1)
#define VTTBR_X_TGRAN_MAGIC 37
#endif

#define VTCR_EL2_FLAGS (VTCR_EL2_COMMON_BITS | VTCR_EL2_TGRAN_FLAGS)
#define VTTBR_X (VTTBR_X_TGRAN_MAGIC - VTCR_EL2_T0SZ_IPA)
/*
* ARM VMSAv8-64 defines an algorithm for finding the translation table
* descriptors in section D4.2.8 in ARM DDI 0487C.a.
*
* The algorithm defines the expectations on the translation table
* addresses for each level, based on PAGE_SIZE, entry level
* and the translation table size (T0SZ). The variable "x" in the
* algorithm determines the alignment of a table base address at a given
* level and thus determines the alignment of VTTBR:BADDR for stage2
* page table entry level.
* Since the number of bits resolved at the entry level could vary
* depending on the T0SZ, the value of "x" is defined based on a
* Magic constant for a given PAGE_SIZE and Entry Level. The
* intermediate levels must be always aligned to the PAGE_SIZE (i.e,
* x = PAGE_SHIFT).
*
* The value of "x" for entry level is calculated as :
* x = Magic_N - T0SZ
*
* where Magic_N is an integer depending on the page size and the entry
* level of the page table as below:
*
* --------------------------------------------
* | Entry level | 4K 16K 64K |
* --------------------------------------------
* | Level: 0 (4 levels) | 28 | - | - |
* --------------------------------------------
* | Level: 1 (3 levels) | 37 | 31 | 25 |
* --------------------------------------------
* | Level: 2 (2 levels) | 46 | 42 | 38 |
* --------------------------------------------
* | Level: 3 (1 level) | - | 53 | 51 |
* --------------------------------------------
*
* We have a magic formula for the Magic_N below:
*
* Magic_N(PAGE_SIZE, Level) = 64 - ((PAGE_SHIFT - 3) * Number_of_levels)
*
* where Number_of_levels = (4 - Level). We are only interested in the
* value for Entry_Level for the stage2 page table.
*
* So, given that T0SZ = (64 - IPA_SHIFT), we can compute 'x' as follows:
*
* x = (64 - ((PAGE_SHIFT - 3) * Number_of_levels)) - (64 - IPA_SHIFT)
* = IPA_SHIFT - ((PAGE_SHIFT - 3) * Number of levels)
*
* Here is one way to explain the Magic Formula:
*
* x = log2(Size_of_Entry_Level_Table)
*
* Since, we can resolve (PAGE_SHIFT - 3) bits at each level, and another
* PAGE_SHIFT bits in the PTE, we have :
*
* Bits_Entry_level = IPA_SHIFT - ((PAGE_SHIFT - 3) * (n - 1) + PAGE_SHIFT)
* = IPA_SHIFT - (PAGE_SHIFT - 3) * n - 3
* where n = number of levels, and since each pointer is 8bytes, we have:
*
* x = Bits_Entry_Level + 3
* = IPA_SHIFT - (PAGE_SHIFT - 3) * n
*
* The only constraint here is that, we have to find the number of page table
* levels for a given IPA size (which we do, see stage2_pt_levels())
*/
#define ARM64_VTTBR_X(ipa, levels) ((ipa) - ((levels) * (PAGE_SHIFT - 3)))

#define VTTBR_BADDR_MASK (((UL(1) << (PHYS_MASK_SHIFT - VTTBR_X)) - 1) << VTTBR_X)
#define VTTBR_VMID_SHIFT (UL(48))
#define VTTBR_VMID_MASK(size) (_AT(u64, (1 << size) - 1) << VTTBR_VMID_SHIFT)

Expand Down
25 changes: 24 additions & 1 deletion arch/arm64/include/asm/kvm_mmu.h
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Original file line number Diff line number Diff line change
Expand Up @@ -145,7 +145,6 @@ static inline unsigned long __kern_hyp_va(unsigned long v)
#define kvm_phys_shift(kvm) KVM_PHYS_SHIFT
#define kvm_phys_size(kvm) (_AC(1, ULL) << kvm_phys_shift(kvm))
#define kvm_phys_mask(kvm) (kvm_phys_size(kvm) - _AC(1, ULL))
#define kvm_vttbr_baddr_mask(kvm) VTTBR_BADDR_MASK

static inline bool kvm_page_empty(void *ptr)
{
Expand Down Expand Up @@ -520,5 +519,29 @@ static inline int hyp_map_aux_data(void)

#define kvm_phys_to_vttbr(addr) phys_to_ttbr(addr)

/*
* Get the magic number 'x' for VTTBR:BADDR of this KVM instance.
* With v8.2 LVA extensions, 'x' should be a minimum of 6 with
* 52bit IPS.
*/
static inline int arm64_vttbr_x(u32 ipa_shift, u32 levels)
{
int x = ARM64_VTTBR_X(ipa_shift, levels);

return (IS_ENABLED(CONFIG_ARM64_PA_BITS_52) && x < 6) ? 6 : x;
}

static inline u64 vttbr_baddr_mask(u32 ipa_shift, u32 levels)
{
unsigned int x = arm64_vttbr_x(ipa_shift, levels);

return GENMASK_ULL(PHYS_MASK_SHIFT - 1, x);
}

static inline u64 kvm_vttbr_baddr_mask(struct kvm *kvm)
{
return vttbr_baddr_mask(kvm_phys_shift(kvm), kvm_stage2_levels(kvm));
}

#endif /* __ASSEMBLY__ */
#endif /* __ARM64_KVM_MMU_H__ */

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