From: Paolo Bonzini <pbonzini@redhat.com>
To: "Chang S. Bae" <chang.seok.bae@intel.com>, seanjc@google.com
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, chao.gao@intel.com
Subject: Re: [PATCH 03/16] KVM: x86: Implement accessors for extended GPRs
Date: Mon, 22 Dec 2025 15:23:34 +0100 [thread overview]
Message-ID: <3607fba6-a519-41a2-9cbb-0d90ef3e6cb7@redhat.com> (raw)
In-Reply-To: <20251221040742.29749-4-chang.seok.bae@intel.com>
On 12/21/25 05:07, Chang S. Bae wrote:
> Add helpers to directly read and write EGPRs (R16–R31).
>
> Unlike legacy GPRs, EGPRs are not cached in vcpu->arch.regs[]. Their
> contents remain live in hardware. If preempted, the EGPR state is
> preserved in the guest XSAVE buffer.
>
> The Advanced Performance Extensions (APX) feature introduces EGPRs as an
> XSAVE-managed state component. The new helpers access the registers
> directly between kvm_fpu_get() and kvm_fpu_put().
>
> Callers should ensure that EGPRs are enabled before using these helpers.
>
> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
> ---
> No change since last version
> ---
> arch/x86/kvm/fpu.h | 80 ++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 78 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/fpu.h b/arch/x86/kvm/fpu.h
> index f2613924532d..f132cad4b49e 100644
> --- a/arch/x86/kvm/fpu.h
> +++ b/arch/x86/kvm/fpu.h
> @@ -148,6 +148,61 @@ static inline void _kvm_write_mmx_reg(int reg, const u64 *data)
> }
> }
>
> +#ifdef CONFIG_X86_64
> +/*
> + * Accessors for extended general-purpose registers. binutils >= 2.43 can
> + * recognize those register symbols.
> + */
> +
> +static inline void _kvm_read_egpr(int reg, unsigned long *data)
> +{
> + /* mov %r16..%r31, %rax */
> + switch (reg) {
> + case __VCPU_XREG_R16: asm(".byte 0xd5, 0x48, 0x89, 0xc0" : "=a"(*data)); break;
> + case __VCPU_XREG_R17: asm(".byte 0xd5, 0x48, 0x89, 0xc8" : "=a"(*data)); break;
> + case __VCPU_XREG_R18: asm(".byte 0xd5, 0x48, 0x89, 0xd0" : "=a"(*data)); break;
> + case __VCPU_XREG_R19: asm(".byte 0xd5, 0x48, 0x89, 0xd8" : "=a"(*data)); break;
> + case __VCPU_XREG_R20: asm(".byte 0xd5, 0x48, 0x89, 0xe0" : "=a"(*data)); break;
> + case __VCPU_XREG_R21: asm(".byte 0xd5, 0x48, 0x89, 0xe8" : "=a"(*data)); break;
> + case __VCPU_XREG_R22: asm(".byte 0xd5, 0x48, 0x89, 0xf0" : "=a"(*data)); break;
> + case __VCPU_XREG_R23: asm(".byte 0xd5, 0x48, 0x89, 0xf8" : "=a"(*data)); break;
> + case __VCPU_XREG_R24: asm(".byte 0xd5, 0x4c, 0x89, 0xc0" : "=a"(*data)); break;
> + case __VCPU_XREG_R25: asm(".byte 0xd5, 0x4c, 0x89, 0xc8" : "=a"(*data)); break;
> + case __VCPU_XREG_R26: asm(".byte 0xd5, 0x4c, 0x89, 0xd0" : "=a"(*data)); break;
> + case __VCPU_XREG_R27: asm(".byte 0xd5, 0x4c, 0x89, 0xd8" : "=a"(*data)); break;
> + case __VCPU_XREG_R28: asm(".byte 0xd5, 0x4c, 0x89, 0xe0" : "=a"(*data)); break;
> + case __VCPU_XREG_R29: asm(".byte 0xd5, 0x4c, 0x89, 0xe8" : "=a"(*data)); break;
> + case __VCPU_XREG_R30: asm(".byte 0xd5, 0x4c, 0x89, 0xf0" : "=a"(*data)); break;
> + case __VCPU_XREG_R31: asm(".byte 0xd5, 0x4c, 0x89, 0xf8" : "=a"(*data)); break;
> + default: BUG();
> + }
> +}
> +
> +static inline void _kvm_write_egpr(int reg, unsigned long *data)
> +{
> + /* mov %rax, %r16...%r31*/
> + switch (reg) {
> + case __VCPU_XREG_R16: asm(".byte 0xd5, 0x18, 0x89, 0xc0" : : "a"(*data)); break;
> + case __VCPU_XREG_R17: asm(".byte 0xd5, 0x18, 0x89, 0xc1" : : "a"(*data)); break;
> + case __VCPU_XREG_R18: asm(".byte 0xd5, 0x18, 0x89, 0xc2" : : "a"(*data)); break;
> + case __VCPU_XREG_R19: asm(".byte 0xd5, 0x18, 0x89, 0xc3" : : "a"(*data)); break;
> + case __VCPU_XREG_R20: asm(".byte 0xd5, 0x18, 0x89, 0xc4" : : "a"(*data)); break;
> + case __VCPU_XREG_R21: asm(".byte 0xd5, 0x18, 0x89, 0xc5" : : "a"(*data)); break;
> + case __VCPU_XREG_R22: asm(".byte 0xd5, 0x18, 0x89, 0xc6" : : "a"(*data)); break;
> + case __VCPU_XREG_R23: asm(".byte 0xd5, 0x18, 0x89, 0xc7" : : "a"(*data)); break;
> + case __VCPU_XREG_R24: asm(".byte 0xd5, 0x19, 0x89, 0xc0" : : "a"(*data)); break;
> + case __VCPU_XREG_R25: asm(".byte 0xd5, 0x19, 0x89, 0xc1" : : "a"(*data)); break;
> + case __VCPU_XREG_R26: asm(".byte 0xd5, 0x19, 0x89, 0xc2" : : "a"(*data)); break;
> + case __VCPU_XREG_R27: asm(".byte 0xd5, 0x19, 0x89, 0xc3" : : "a"(*data)); break;
> + case __VCPU_XREG_R28: asm(".byte 0xd5, 0x19, 0x89, 0xc4" : : "a"(*data)); break;
> + case __VCPU_XREG_R29: asm(".byte 0xd5, 0x19, 0x89, 0xc5" : : "a"(*data)); break;
> + case __VCPU_XREG_R30: asm(".byte 0xd5, 0x19, 0x89, 0xc6" : : "a"(*data)); break;
> + case __VCPU_XREG_R31: asm(".byte 0xd5, 0x19, 0x89, 0xc7" : : "a"(*data)); break;
> + default: BUG();
> + }
> +}
> +#endif
These are also way too big for inlining; move them in x86.c. Already in
patch 2,
+#ifdef CONFIG_X86_64
+static inline unsigned long kvm_read_egpr(int reg) { return 0; }
+static inline void kvm_write_egpr(int reg, unsigned long data) { }
+#endif
can be in x86.c.
Paolo
> static inline void kvm_fpu_get(void)
> {
> fpregs_lock();
> @@ -205,8 +260,29 @@ static inline void kvm_write_mmx_reg(int reg, const u64 *data)
> }
>
> #ifdef CONFIG_X86_64
> -static inline unsigned long kvm_read_egpr(int reg) { return 0; }
> -static inline void kvm_write_egpr(int reg, unsigned long data) { }
> +static inline unsigned long kvm_read_egpr(int reg)
> +{
> + unsigned long data;
> +
> + if (WARN_ON_ONCE(!cpu_has_xfeatures(XFEATURE_MASK_APX, NULL)))
> + return 0;
> +
> + kvm_fpu_get();
> + _kvm_read_egpr(reg, &data);
> + kvm_fpu_put();
> +
> + return data;
> +}
> +
> +static inline void kvm_write_egpr(int reg, unsigned long data)
> +{
> + if (WARN_ON_ONCE(!cpu_has_xfeatures(XFEATURE_MASK_APX, NULL)))
> + return;
> +
> + kvm_fpu_get();
> + _kvm_write_egpr(reg, &data);
> + kvm_fpu_put();
> +}
> #endif
>
> #endif
next prev parent reply other threads:[~2025-12-22 14:23 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-21 4:07 [PATCH 00/16] KVM: x86: Enable APX for guests Chang S. Bae
2025-12-21 4:07 ` [PATCH 01/16] KVM: x86: Rename register accessors to be GPR-specific Chang S. Bae
2025-12-21 4:07 ` [PATCH 02/16] KVM: x86: Refactor GPR accessors to differentiate register access types Chang S. Bae
2025-12-21 4:07 ` [PATCH 03/16] KVM: x86: Implement accessors for extended GPRs Chang S. Bae
2025-12-22 14:23 ` Paolo Bonzini [this message]
2025-12-21 4:07 ` [PATCH 04/16] KVM: VMX: Introduce unified instruction info structure Chang S. Bae
2025-12-21 4:07 ` [PATCH 05/16] KVM: VMX: Refactor instruction information retrieval Chang S. Bae
2025-12-21 4:07 ` [PATCH 06/16] KVM: VMX: Refactor GPR index retrieval from exit qualification Chang S. Bae
2025-12-21 4:07 ` [PATCH 07/16] KVM: nVMX: Propagate the extended instruction info field Chang S. Bae
2025-12-31 1:38 ` Chao Gao
2025-12-21 4:07 ` [PATCH 08/16] KVM: VMX: Support extended register index in exit handling Chang S. Bae
2025-12-26 5:27 ` Chao Gao
2025-12-21 4:07 ` [PATCH 09/16] KVM: emulate: Support EGPR accessing and tracking Chang S. Bae
2025-12-21 4:07 ` [PATCH 10/16] KVM: emulate: Handle EGPR index and REX2-incompatible opcodes Chang S. Bae
2025-12-22 14:36 ` Paolo Bonzini
2025-12-21 4:07 ` [PATCH 11/16] KVM: emulate: Support REX2-prefixed opcode decode Chang S. Bae
2025-12-21 4:07 ` [PATCH 12/16] KVM: emulate: Reject EVEX-prefixed instructions Chang S. Bae
2025-12-21 4:07 ` [PATCH 13/16] KVM: x86: Guard valid XCR0.APX settings Chang S. Bae
2025-12-21 4:07 ` [PATCH 14/16] KVM: x86: Expose APX foundational feature bit to guests Chang S. Bae
2025-12-21 4:07 ` [PATCH 15/16] KVM: x86: Expose APX sub-features " Chang S. Bae
2025-12-21 4:07 ` [PATCH 16/16] KVM: x86: selftests: Add APX state handling and XCR0 sanity checks Chang S. Bae
2025-12-22 14:53 ` [PATCH 00/16] KVM: x86: Enable APX for guests Paolo Bonzini
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