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KVM: x86: Add helper to retrieve current value of user return MSR

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In the user return MSR support, the cached value is always the hardware
value of the specific MSR. Therefore, add a helper to retrieve the
cached value, which can replace the need for RDMSR, for example, to
allow SEV-ES guests to restore the correct host hardware value without
using RDMSR.

Cc: stable@vger.kernel.org
Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
[sean: drop "cache" from the name, make it a one-liner, tag for stable]
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20250923153738.1875174-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Hou Wenlong 2025-09-23 08:37:37 -07:00 committed by Sean Christopherson
parent 5b66e335ea
commit 9bc3663507
2 changed files with 7 additions and 0 deletions
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1
arch/x86/include/asm/kvm_host.h
View File

@ -2357,6 +2357,7 @@ int kvm_add_user_return_msr(u32 msr);
int kvm_find_user_return_msr(u32 msr);
int kvm_set_user_return_msr(unsigned index, u64 val, u64 mask);
void kvm_user_return_msr_update_cache(unsigned int index, u64 val);
u64 kvm_get_user_return_msr(unsigned int slot);
static inline bool kvm_is_supported_user_return_msr(u32 msr)
{

6
arch/x86/kvm/x86.c
View File

@ -677,6 +677,12 @@ void kvm_user_return_msr_update_cache(unsigned int slot, u64 value)
}
EXPORT_SYMBOL_GPL(kvm_user_return_msr_update_cache);
u64 kvm_get_user_return_msr(unsigned int slot)
{
return this_cpu_ptr(user_return_msrs)->values[slot].curr;
}
EXPORT_SYMBOL_GPL(kvm_get_user_return_msr);
static void drop_user_return_notifiers(void)
{
struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);