From: Dave Hansen <dave.hansen@intel.com>
To: Marc Orr <marcorr@google.com>
Cc: kvm@vger.kernel.org, Jim Mattson <jmattson@google.com>,
David Rientjes <rientjes@google.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
linux-mm@kvack.org, akpm@linux-foundation.org,
pbonzini@redhat.com, rkrcmar@redhat.com, willy@infradead.org,
sean.j.christopherson@intel.com, dave.hansen@linux.intel.com,
Wanpeng Li <kernellwp@gmail.com>
Subject: Re: [kvm PATCH v5 2/4] kvm: x86: Dynamically allocate guest_fpu
Date: Wed, 31 Oct 2018 14:44:11 -0700 [thread overview]
Message-ID: <6ebffd2a-a387-ed71-1514-6dff42a35bec@intel.com> (raw)
In-Reply-To: <CAA03e5FBri+LSZoGKJpJJruSEoNZ39DTbJMRhJbatgQAs6BiaA@mail.gmail.com>
On 10/31/18 2:39 PM, Marc Orr wrote:
> That makes sense. But my specific concern is the code I've copied
> below, from arch/x86/kvm/x86.c. Notice on a system where
> guest_fpu.state is a fregs_state, this code would generate garbage for
> some fields. With the new code we're talking about, it will cause
> memory corruption. But maybe it's not possible to run this code on a
> system with an fregs_state, because such systems would predate VMX?
Ahh, got it.
So, you *can* clear X86_FEATURE_* bits from the kernel command-line, so
it's theoretically possible to have a system that supports VMX, but
doesn't support a modern MMU. It's obviously not well tested. :)
The KVM code you pasted, to be "correct" should probably be checking
X86_FEATURE_FXSR and X86_FEATURE_FPU *somewhere*.
next prev parent reply other threads:[~2018-10-31 21:44 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-31 13:26 [kvm PATCH v5 0/4] shrink vcpu_vmx down to order 2 Marc Orr
2018-10-31 13:26 ` [kvm PATCH v5 1/4] kvm: x86: Use task structs fpu field for user Marc Orr
2018-10-31 13:26 ` [kvm PATCH v5 2/4] kvm: x86: Dynamically allocate guest_fpu Marc Orr
2018-10-31 14:11 ` Dave Hansen
2018-10-31 21:13 ` Marc Orr
2018-10-31 21:21 ` Dave Hansen
2018-10-31 21:24 ` Marc Orr
2018-10-31 21:30 ` Dave Hansen
2018-10-31 21:39 ` Marc Orr
2018-10-31 21:44 ` Dave Hansen [this message]
2018-10-31 13:26 ` [kvm PATCH v5 3/4] kvm: vmx: refactor vmx_msrs struct for vmalloc Marc Orr
2018-10-31 14:12 ` Dave Hansen
2018-10-31 14:15 ` Sean Christopherson
2018-10-31 14:19 ` Marc Orr
2018-10-31 13:26 ` [kvm PATCH v5 4/4] kvm: vmx: use vmalloc() to allocate vcpus Marc Orr
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