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 14:21:27 -0700 [thread overview]
Message-ID: <4094fe59-a161-99f0-e3cd-7ac14eb9f5a4@intel.com> (raw)
In-Reply-To: <CAA03e5HmMq-+9WsJ+Kd05ary85A7HJ5HJbNMUzc87QCRxamJGg@mail.gmail.com>
On 10/31/18 2:13 PM, Marc Orr wrote:
> KVM explicitly cast guest_fpu.state as a fxregs_state in a few
> places (e.g., the ioctls). Yet, I see a code path in
> fpu__init_system_xstate_size_legacy() that sets
> fpu_kernel_xstate_size to sizeof(struct fregs_state). Will this cause
> problems? You mentioned that the fpu's state field is expected to
> range from ~500 bytes to ~3k, which implies that it should never get
> set to sizeof(struct fregs_state). But I want to confirm.
It can get set to sizeof(struct fregs_state) for systems where XSAVE is
not in use. I was neglecting to mention those when I said the "~500
byte" number.
My point was that it can vary wildly and that any static allocation
scheme will waste lots of memory when we have small hardware-supported
buffers.
next prev parent reply other threads:[~2018-10-31 21:21 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 [this message]
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
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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