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KVM: arm64: Use CAST instruction for swapping guest descriptor

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Use the CAST instruction to swap the guest descriptor when FEAT_LSUI
is enabled, avoiding the need to clear the PAN bit.

FEAT_LSUI is introduced in Armv9.6, where FEAT_PAN is mandatory. However,
this assumption may not always hold:

 - Some CPUs may advertise FEAT_LSUI but lack FEAT_PAN.
 - Virtualization or ID register overrides may expose invalid feature
   combinations.

Therefore, instead of disabling FEAT_LSUI when FEAT_PAN is absent, wrap
LSUI instructions with uaccess_ttbr0_enable()/disable() when
ARM64_SW_TTBR0_PAN is enabled.

Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Yeoreum Yun
2026-03-14 17:51:32 +00:00
committed by Catalin Marinas
parent 44adf2bf40
commit 16dbe77a5b
1 changed files with 33 additions and 1 deletions
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34
arch/arm64/kvm/at.c
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@@ -9,6 +9,7 @@
#include <asm/esr.h>
#include <asm/kvm_hyp.h>
#include <asm/kvm_mmu.h>
#include <asm/lsui.h>
static void fail_s1_walk(struct s1_walk_result *wr, u8 fst, bool s1ptw)
{
@@ -1681,6 +1682,35 @@ int __kvm_find_s1_desc_level(struct kvm_vcpu *vcpu, u64 va, u64 ipa, int *level)
}
}
static int __lsui_swap_desc(u64 __user *ptep, u64 old, u64 new)
{
u64 tmp = old;
int ret = 0;
/*
* Wrap LSUI instructions with uaccess_ttbr0_enable()/disable(),
* as PAN toggling is not required.
*/
uaccess_ttbr0_enable();
asm volatile(__LSUI_PREAMBLE
"1: cast %[old], %[new], %[addr]\n"
"2:\n"
_ASM_EXTABLE_UACCESS_ERR(1b, 2b, %w[ret])
: [old] "+r" (old), [addr] "+Q" (*ptep), [ret] "+r" (ret)
: [new] "r" (new)
: "memory");
uaccess_ttbr0_disable();
if (ret)
return ret;
if (tmp != old)
return -EAGAIN;
return ret;
}
static int __lse_swap_desc(u64 __user *ptep, u64 old, u64 new)
{
u64 tmp = old;
@@ -1756,7 +1786,9 @@ int __kvm_at_swap_desc(struct kvm *kvm, gpa_t ipa, u64 old, u64 new)
return -EPERM;
ptep = (u64 __user *)hva + offset;
if (cpus_have_final_cap(ARM64_HAS_LSE_ATOMICS))
if (cpus_have_final_cap(ARM64_HAS_LSUI))
r = __lsui_swap_desc(ptep, old, new);
else if (cpus_have_final_cap(ARM64_HAS_LSE_ATOMICS))
r = __lse_swap_desc(ptep, old, new);
else
r = __llsc_swap_desc(ptep, old, new);