10000 Refactored the PMP address check for RV32 vs RV64 by ZhekaS · Pull Request #4414 · tock/tock · GitHub
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Refactored the PMP address check for RV32 vs RV64 #4414

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Merged
merged 2 commits into from
May 6, 2025
Merged

Refactored the PMP address check for RV32 vs RV64 #4414

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5501be0
Refactored the PMP address check for RV32 vs RV64
Apr 25, 2025
f89f04f
Changed the mask name, updated doc-comment
May 6, 2025
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52 changes: 21 additions & 31 deletions arch/riscv/src/pmp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -35,15 +35,18 @@ register_bitfields![u8,
]
];

/// Mask for valid values of the `pmpaddrX` CSRs on RV64 platforms.
/// Mask for valid values of the `pmpaddrX` CSRs on RISCV platforms.
///
/// RV64 platforms support only a 56 bit physical address space. For this reason
/// (and because addresses in `pmpaddrX` CSRs are left-shifted by 2 bit) the
/// uppermost 10 bits of a `pmpaddrX` CSR are defined as WARL-0. ANDing with
/// this mask achieves the same effect; thus it can be used to determine whether
/// a given PMP region spec would be legal and applied before writing it to a
/// `pmpaddrX` CSR.
const PMPADDR_RV64_MASK: u64 = 0x003F_FFFF_FFFF_FFFF;
/// `pmpaddrX` CSR. For RV32 platforms, th whole 32 bit address range is valid.
///
/// This mask will have the value `0x003F_FFFF_FFFF_FFFF` on RV64 platforms, and
/// `0xFFFFFFFF` on RV32 platforms.
const PMPADDR_MASK: usize = (0x003F_FFFF_FFFF_FFFFu64 & usize::MAX as u64) as usize;

/// A `pmpcfg` octet for a user-mode (non-locked) TOR-addressed PMP region.
///
Expand Down Expand Up @@ -142,14 +145,11 @@ impl NAPOTRegionSpec {
/// rejects the `pmpaddr` (tests whether any of the 10 most significant bits
/// are non-zero).
pub fn from_pmpaddr_csr(pmpaddr: usize) -> Option<Self> {
// On 64-bit platforms, the 10 most significant bits must be 0:
if core::mem::size_of::<usize>() == core::mem::size_of::<u64>() {
if (pmpaddr as u64) & !PMPADDR_RV64_MASK != 0 {
return None;
}
}

Some(NAPOTRegionSpec { pmpaddr })
// On 64-bit platforms, the 10 most significant bits must be 0
// Prevent the `&-masking with zero` lint error in case of RV32
// The redundant checks in this case are optimized out by the compiler on any 1-3,z opt-level
#[allow(clippy::bad_bit_mask)]
(pmpaddr & !PMPADDR_MASK == 0).then_some(NAPOTRegionSpec { pmpaddr })
}

/// Construct a new [`NAPOTRegionSpec`] from a start address and size.
Expand Down Expand Up @@ -241,26 +241,16 @@ impl TORRegionSpec {
/// this case, returns `None` (tests whether any of the 10 most significant
/// bits of either `pmpaddr` are non-zero).
pub fn from_pmpaddr_csrs(pmpaddr_a: usize, pmpaddr_b: usize) -> Option<TORRegionSpec> {
if pmpaddr_a >= pmpaddr_b {
return None;
}

// On 64-bit platforms, the 10 most significant bits must be 0:
if core::mem::size_of::<usize>() == core::mem::size_of::<u64>() {
// Checking pmpaddr_b should be sufficient (as it must be greater),
// but we'll leave it up to the compiler to be smart enough to
// figure that out:
if (pmpaddr_a as u64) & !PMPADDR_RV64_MASK != 0
|| (pmpaddr_b as u64) & !PMPADDR_RV64_MASK != 0
{
return None;
}
}

Some(TORRegionSpec {
pmpaddr_a,
pmpaddr_b,
})
// Prevent the `&-masking with zero` lint error in case of RV32
// The redundant checks in this case are optimized out by the compiler on any 1-3,z opt-level
#[allow(clippy::bad_bit_mask)]
((pmpaddr_a < pmpaddr_b)
&& (pmpaddr_a & !PMPADDR_MASK == 0)
&& (pmpaddr_b & !PMPADDR_MASK == 0))
.then_some(TORRegionSpec {
pmpaddr_a,
pmpaddr_b,
})
}

/// Construct a new [`TORRegionSpec`] from a range of addresses.
Expand Down
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