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KVM: x86: Use a proper bitmap for tracking available/dirty registers

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Define regs_{avail,dirty} as bitmaps instead of U32s to harden against
overflow, and to allow for dynamically sizing the bitmaps when APX comes
along, which will add 16 more GPRs (R16-R31) and thus increase the total
number of registers beyond 32.

Open code writes in the "reset" APIs, as the writes are hot paths and
bitmap_write() is complete overkill for what KVM needs.  Even better,
hardcoding writes to entry '0' in the array is a perfect excuse to assert
that the array contains exactly one entry, e.g. to effectively add guard
against defining R16-R31 in 32-bit kernels.

For all intents and purposes, no functional change intended even though
using bitmap_fill() will mean "undefined" registers are no longer marked
available and dirty (KVM should never be querying those bits).

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Tested-by: Kai Huang <kai.huang@intel.com>
Message-ID: <20260409224236.2021562-7-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2026-04-09 15:42:35 -07:00 committed by Paolo Bonzini
parent 133ecccbfe
commit 39a5ee37be
3 changed files with 18 additions and 12 deletions
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6
arch/x86/include/asm/kvm_host.h
View File

@ -211,6 +211,8 @@ enum kvm_reg {
VCPU_REG_SEGMENTS,
VCPU_REG_EXIT_INFO_1,
VCPU_REG_EXIT_INFO_2,
NR_VCPU_TOTAL_REGS,
};
enum {
@ -802,8 +804,8 @@ struct kvm_vcpu_arch {
*/
unsigned long regs[NR_VCPU_GENERAL_PURPOSE_REGS];
unsigned long rip;
unsigned long regs_avail;
unsigned long regs_dirty;
DECLARE_BITMAP(regs_avail, NR_VCPU_TOTAL_REGS);
DECLARE_BITMAP(regs_dirty, NR_VCPU_TOTAL_REGS);
unsigned long cr0;
unsigned long cr0_guest_owned_bits;

20
arch/x86/kvm/kvm_cache_regs.h
View File

@ -67,29 +67,29 @@ static inline bool kvm_register_is_available(struct kvm_vcpu *vcpu,
enum kvm_reg reg)
{
kvm_assert_register_caching_allowed(vcpu);
return test_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
return test_bit(reg, vcpu->arch.regs_avail);
}
static inline bool kvm_register_is_dirty(struct kvm_vcpu *vcpu,
enum kvm_reg reg)
{
kvm_assert_register_caching_allowed(vcpu);
return test_bit(reg, (unsigned long *)&vcpu->arch.regs_dirty);
return test_bit(reg, vcpu->arch.regs_dirty);
}
static inline void kvm_register_mark_available(struct kvm_vcpu *vcpu,
enum kvm_reg reg)
{
kvm_assert_register_caching_allowed(vcpu);
__set_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
__set_bit(reg, vcpu->arch.regs_avail);
}
static inline void kvm_register_mark_dirty(struct kvm_vcpu *vcpu,
enum kvm_reg reg)
{
kvm_assert_register_caching_allowed(vcpu);
__set_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
__set_bit(reg, (unsigned long *)&vcpu->arch.regs_dirty);
__set_bit(reg, vcpu->arch.regs_avail);
__set_bit(reg, vcpu->arch.regs_dirty);
}
/*
@ -102,12 +102,15 @@ static __always_inline bool kvm_register_test_and_mark_available(struct kvm_vcpu
enum kvm_reg reg)
{
kvm_assert_register_caching_allowed(vcpu);
return arch___test_and_set_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);
return arch___test_and_set_bit(reg, vcpu->arch.regs_avail);
}
static __always_inline void kvm_clear_available_registers(struct kvm_vcpu *vcpu,
unsigned long clear_mask)
{
BUILD_BUG_ON(sizeof(clear_mask) != sizeof(vcpu->arch.regs_avail[0]));
BUILD_BUG_ON(ARRAY_SIZE(vcpu->arch.regs_avail) != 1);
/*
* Note the bitwise-AND! In practice, a straight write would also work
* as KVM initializes the mask to all ones and never clears registers
@ -115,12 +118,13 @@ static __always_inline void kvm_clear_available_registers(struct kvm_vcpu *vcpu,
* sanity checking as incorrectly marking an eagerly sync'd register
* unavailable will generate a WARN due to an unexpected cache request.
*/
vcpu->arch.regs_avail &= ~clear_mask;
vcpu->arch.regs_avail[0] &= ~clear_mask;
}
static __always_inline void kvm_reset_dirty_registers(struct kvm_vcpu *vcpu)
{
vcpu->arch.regs_dirty = 0;
BUILD_BUG_ON(ARRAY_SIZE(vcpu->arch.regs_dirty) != 1);
vcpu->arch.regs_dirty[0] = 0;
}
/*

4
arch/x86/kvm/x86.c
View File

@ -12836,8 +12836,8 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
int r;
vcpu->arch.last_vmentry_cpu = -1;
vcpu->arch.regs_avail = ~0;
vcpu->arch.regs_dirty = ~0;
bitmap_fill(vcpu->arch.regs_avail, NR_VCPU_TOTAL_REGS);
bitmap_fill(vcpu->arch.regs_dirty, NR_VCPU_TOTAL_REGS);
kvm_gpc_init(&vcpu->arch.pv_time, vcpu->kvm);