Re: [PATCH v7 6/8] KVM: MMU: Add support for PKS emulation
From: Wang, Lei
Date: Fri May 27 2022 - 05:40:44 EST
On 5/25/2022 7:28 AM, Sean Christopherson wrote:
On Sun, Apr 24, 2022, Lei Wang wrote:
@@ -454,10 +455,11 @@ struct kvm_mmu {
u8 permissions[16];
/*
- * The pkru_mask indicates if protection key checks are needed. It
- * consists of 16 domains indexed by page fault error code bits [4:1],
- * with PFEC.RSVD replaced by ACC_USER_MASK from the page tables.
- * Each domain has 2 bits which are ANDed with AD and WD from PKRU.
+ * The pkr_mask indicates if protection key checks are needed.
+ * It consists of 16 domains indexed by page fault error code
+ * bits[4:1] with PFEC.RSVD replaced by ACC_USER_MASK from the
+ * page tables. Each domain has 2 bits which are ANDed with AD
+ * and WD from PKRU/PKRS.
Same comments, align and wrap closer to 80 please.
Will do it.
*/
u32 pkr_mask;
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index cea03053a153..6963c641e6ce 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -45,7 +45,8 @@
#define PT32E_ROOT_LEVEL 3
#define KVM_MMU_CR4_ROLE_BITS (X86_CR4_PSE | X86_CR4_PAE | X86_CR4_LA57 | \
- X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_PKE)
+ X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_PKE | \
+ X86_CR4_PKS)
#define KVM_MMU_CR0_ROLE_BITS (X86_CR0_PG | X86_CR0_WP)
#define KVM_MMU_EFER_ROLE_BITS (EFER_LME | EFER_NX)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6d3276986102..a6cbc22d3312 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -209,6 +209,7 @@ BUILD_MMU_ROLE_REGS_ACCESSOR(cr4, smep, X86_CR4_SMEP);
BUILD_MMU_ROLE_REGS_ACCESSOR(cr4, smap, X86_CR4_SMAP);
BUILD_MMU_ROLE_REGS_ACCESSOR(cr4, pke, X86_CR4_PKE);
BUILD_MMU_ROLE_REGS_ACCESSOR(cr4, la57, X86_CR4_LA57);
+BUILD_MMU_ROLE_REGS_ACCESSOR(cr4, pks, X86_CR4_PKS);
BUILD_MMU_ROLE_REGS_ACCESSOR(efer, nx, EFER_NX);
BUILD_MMU_ROLE_REGS_ACCESSOR(efer, lma, EFER_LMA);
@@ -231,6 +232,7 @@ BUILD_MMU_ROLE_ACCESSOR(ext, cr4, smep);
BUILD_MMU_ROLE_ACCESSOR(ext, cr4, smap);
BUILD_MMU_ROLE_ACCESSOR(ext, cr4, pke);
BUILD_MMU_ROLE_ACCESSOR(ext, cr4, la57);
+BUILD_MMU_ROLE_ACCESSOR(ext, cr4, pks);
BUILD_MMU_ROLE_ACCESSOR(base, efer, nx);
static struct kvm_mmu_role_regs vcpu_to_role_regs(struct kvm_vcpu *vcpu)
@@ -4608,37 +4610,58 @@ static void update_permission_bitmask(struct kvm_mmu *mmu, bool ept)
}
/*
...
+ * Protection Key Rights (PKR) is an additional mechanism by which data accesses
+ * with 4-level or 5-level paging (EFER.LMA=1) may be disabled based on the
+ * Protection Key Rights Userspace (PRKU) or Protection Key Rights Supervisor
+ * (PKRS) registers. The Protection Key (PK) used for an access is a 4-bit
+ * value specified in bits 62:59 of the leaf PTE used to translate the address.
+ *
+ * PKRU and PKRS are 32-bit registers, with 16 2-bit entries consisting of an
+ * access-disable (AD) and write-disable (WD) bit. The PK from the leaf PTE is
+ * used to index the approriate PKR (see below), e.g. PK=1 would consume bits
s/approriate/appropriate
Will correct it.
+ * 3:2 (bit 3 == write-disable, bit 2 == access-disable).
+ *
+ * The PK register (PKRU vs. PKRS) indexed by the PK depends on the type of
+ * _address_ (not access type!). For a user-mode address, PKRU is used; for a
+ * supervisor-mode address, PKRS is used. An address is supervisor-mode if the
+ * U/S flag (bit 2) is 0 in at least one of the paging-structure entries, i.e.
+ * an address is user-mode if the U/S flag is 1 in _all_ entries. Again, this
+ * is the address type, not the the access type, e.g. a supervisor-mode _access_
Double "the the" can be a single "the".
Will remove it.
+ * will consume PKRU if the _address_ is a user-mode address.
+ *
+ * As alluded to above, PKR checks are only performed for data accesses; code
+ * fetches are not subject to PKR checks. Terminal page faults (!PRESENT or
+ * PFEC.RSVD=1) are also not subject to PKR checks.
+ *
+ * PKR write-disable checks for superivsor-mode _accesses_ are performed if and
+ * only if CR0.WP=1 (though access-disable checks still apply).
+ *
+ * In summary, PKR checks are based on (a) EFER.LMA, (b) CR4.PKE or CR4.PKS,
+ * (c) CR0.WP, (d) the PK in the leaf PTE, (e) two bits from the corresponding
+ * PKR{S,U} entry, (f) the access type (derived from the other PFEC bits), and
+ * (g) the address type (retrieved from the paging-structure entries).
+ *
+ * To avoid conditional branches in permission_fault(), the PKR bitmask caches
+ * the above inputs, except for (e) the PKR{S,U} entry. The FETCH, USER, and
+ * WRITE bits of the PFEC and the effective value of the paging-structures' U/S
+ * bit (slotted into the PFEC.RSVD position, bit 3) are used to index into the
+ * PKR bitmask (similar to the 4-bit Protection Key itself). The two bits of
+ * the PKR bitmask "entry" are then extracted and ANDed with the two bits of
+ * the PKR{S,U} register corresponding to the address type and protection key.
+ *
+ * E.g. for all values where PFEC.FETCH=1, the corresponding pkr_bitmask bits
+ * will be 00b, thus masking away the AD and WD bits from the PKR{S,U} register
+ * to suppress PKR checks on code fetches.
+ */
static void update_pkr_bitmask(struct kvm_mmu *mmu)
{
unsigned bit;
bool wp;
-
Please keep this newline, i.e. after the declaration of the cr4 booleans. That
helps isolate the clearing of mmu->pkr_mask, which makes the functional affect of
the earlier return more obvious.
Ah, and use reverse fir tree for the variable declarations, i.e.
bool cr4_pke = is_cr4_pke(mmu);
bool cr4_pks = is_cr4_pks(mmu);
unsigned bit;
bool wp;
mmu->pkr_mask = 0;
if (!cr4_pke && !cr4_pks)
return;
Very nice of you, will use reverse fir tree for the declaration.
+ bool cr4_pke = is_cr4_pke(mmu);
+ bool cr4_pks = is_cr4_pks(mmu);
mmu->pkr_mask = 0;
- if (!is_cr4_pke(mmu))
+ if (!cr4_pke && !cr4_pks)
return;
wp = is_cr0_wp(mmu);
...
@@ -6482,14 +6509,22 @@ u32 kvm_mmu_pkr_bits(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
unsigned pte_access, unsigned pte_pkey, unsigned int pfec)
{
u32 pkr_bits, offset;
+ u32 pkr;
/*
- * PKRU defines 32 bits, there are 16 domains and 2
- * attribute bits per domain in pkru. pte_pkey is the
- * index of the protection domain, so pte_pkey * 2 is
- * is the index of the first bit for the domain.
+ * PKRU and PKRS both define 32 bits. There are 16 domains
+ * and 2 attribute bits per domain in them. pte_key is the
+ * index of the protection domain, so pte_pkey * 2 is the
+ * index of the first bit for the domain. The use of PKRU
+ * versus PKRS is selected by the address type, as determined
+ * by the U/S bit in the paging-structure entries.
Align and wrap closer to 80 please.
Will do it.