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Peter Anvin" , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Thu, Sep 18, 2025, Hou Wenlong wrote: > 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. > > Signed-off-by: Hou Wenlong > --- > arch/x86/include/asm/kvm_host.h | 1 + > arch/x86/kvm/x86.c | 8 ++++++++ > 2 files changed, 9 insertions(+) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index cb86f3cca3e9..2cbb0f446a9b 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -2376,6 +2376,7 @@ 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_cache(unsigned int index); s/index/slot (the existing helpers need to be changed). The user_return APIs deliberately use "slot" to try and make it more obvious that they take the slot within the array, not the index of the MSR. > static inline bool kvm_is_supported_user_return_msr(u32 msr) > { > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 6d85fbafc679..88d26c86c3b2 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -675,6 +675,14 @@ 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_cache(unsigned int slot) I vote to drop "cache". I don't love the existing kvm_user_return_msr_update_cache() name (or implementation). I would much rather that code be (I'll post a separate patch) the below, to capture that the "cache" version is performing a subest of the kvm_set_user_return_msr(). void __kvm_set_user_return_msr(unsigned int slot, u64 value) { struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs); msrs->values[slot].curr = value; kvm_user_return_register_notifier(msrs); } EXPORT_SYMBOL_GPL(__kvm_set_user_return_msr); int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask) { struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs); int err; value = (value & mask) | (msrs->values[slot].host & ~mask); if (value == msrs->values[slot].curr) return 0; err = wrmsrq_safe(kvm_uret_msrs_list[slot], value); if (err) return 1; __kvm_set_user_return_msr(slot, value); return 0; } EXPORT_SYMBOL_GPL(kvm_set_user_return_msr); > +{ > + struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs); > + > + return msrs->values[slot].curr; This can be a one-liner. How about this? --- arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/x86.c | 6 ++++++ 2 files changed, 7 insertions(+) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 17772513b9cc..14236006266b 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -2376,6 +2376,7 @@ 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) { diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index e07936efacd4..801bf6172a21 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -675,6 +675,12 @@ 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); base-commit: c8fbf7ceb2ae3f64b0c377c8c21f6df577a13eb4 --