Messages in this thread | | | Date | Tue, 22 Nov 2016 10:12:54 -0500 (EST) | From | Paolo Bonzini <> | Subject | Re: [PATCH v1 2/3] kvm: svm: Add kvm_fast_pio_in support |
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----- Original Message ----- > From: "Tom Lendacky" <thomas.lendacky@amd.com> > To: "Paolo Bonzini" <pbonzini@redhat.com>, "Brijesh Singh" <brijesh.singh@amd.com>, kvm@vger.kernel.org > Cc: rkrcmar@redhat.com, joro@8bytes.org, x86@kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, > hpa@zytor.com, tglx@linutronix.de, bp@suse.de > Sent: Tuesday, November 22, 2016 3:25:52 PM > Subject: Re: [PATCH v1 2/3] kvm: svm: Add kvm_fast_pio_in support > > On 11/21/2016 8:50 AM, Paolo Bonzini wrote: > > > > > > On 14/11/2016 23:15, Brijesh Singh wrote: > >> + /* For size less than 4 we merge, else we zero extend */ > >> + val = (size < 4) ? kvm_register_read(vcpu, VCPU_REGS_RAX) : 0; > > > > Are you sure it shouldn't always zero extend the high 32-bits? So "val" > > should be declared as u32. > > > > Paolo > > It should only zero extend when dealing with a 32-bit operation. Any use > of 8 or 16 bit registers leaves the upper 56 or 48 bits as is (see > section 3.1.2.3 in http://support.amd.com/TechDocs/24592.pdf).
Duh, right, see also assign_register in arch/x86/kvm/emulate.c.
Paolo
> Thanks, > Tom > > > > >> + ret = emulator_pio_in_emulated(&vcpu->arch.emulate_ctxt, size, port, > >> + &val, 1); > >> + if (ret) { > >> + kvm_register_write(vcpu, VCPU_REGS_RAX, val); > >> + return ret; > >> + } >
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