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Groups > linux.kernel > #1652733
| From | Nick Desaulniers <nick.desaulniers@gmail.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH v4] KVM: x86: avoid large stack allocations in em_fxrstor |
| Date | 2017-05-30 00:50 +0200 |
| Message-ID | <tMBE5-6CW-5@gated-at.bofh.it> (permalink) |
| References | <tMzCh-5cQ-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
em_fxstor previously called fxstor_fixup. Both created instances of
struct fxregs_state on the stack, which triggered the warning:
arch/x86/kvm/emulate.c:4018:12: warning: stack frame size of 1080 bytes
in function
'em_fxrstor' [-Wframe-larger-than=]
static int em_fxrstor(struct x86_emulate_ctxt *ctxt)
^
with CONFIG_FRAME_WARN set to 1024.
This patch does the fixup in em_fxstor now, avoiding one additional
struct fxregs_state, and now fxstor_fixup can be removed as it has no
other call sites.
Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
---
New in V4:
* undo changes for V3, prefer to only call segmented_read_std() when
size has been initialized.
New in V3:
* initialized size to 0 to avoid maybe-uninitialized warning. Check
that it gets set to something other than 0 before passing size to
segmented_read_std().
New in V2:
* reworked patch to do what was recommended by maintainers in:
https://lkml.org/lkml/2017/5/25/391
arch/x86/kvm/emulate.c | 64 ++++++++++++++++++++------------------------------
1 file changed, 26 insertions(+), 38 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 0816ab2e8adc..0367f7f81792 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3985,57 +3985,45 @@ static int em_fxsave(struct x86_emulate_ctxt *ctxt)
return segmented_write_std(ctxt, ctxt->memop.addr.mem, &fx_state, size);
}
-static int fxrstor_fixup(struct x86_emulate_ctxt *ctxt,
- struct fxregs_state *new)
-{
- int rc = X86EMUL_CONTINUE;
- struct fxregs_state old;
-
- rc = asm_safe("fxsave %[fx]", , [fx] "+m"(old));
- if (rc != X86EMUL_CONTINUE)
- return rc;
-
- /*
- * 64 bit host will restore XMM 8-15, which is not correct on non-64
- * bit guests. Load the current values in order to preserve 64 bit
- * XMMs after fxrstor.
- */
-#ifdef CONFIG_X86_64
- /* XXX: accessing XMM 8-15 very awkwardly */
- memcpy(&new->xmm_space[8 * 16/4], &old.xmm_space[8 * 16/4], 8 * 16);
-#endif
-
- /*
- * Hardware doesn't save and restore XMM 0-7 without CR4.OSFXSR, but
- * does save and restore MXCSR.
- */
- if (!(ctxt->ops->get_cr(ctxt, 4) & X86_CR4_OSFXSR))
- memcpy(new->xmm_space, old.xmm_space, 8 * 16);
-
- return rc;
-}
-
static int em_fxrstor(struct x86_emulate_ctxt *ctxt)
{
struct fxregs_state fx_state;
int rc;
+ unsigned int size;
rc = check_fxsr(ctxt);
if (rc != X86EMUL_CONTINUE)
return rc;
- rc = segmented_read_std(ctxt, ctxt->memop.addr.mem, &fx_state, 512);
- if (rc != X86EMUL_CONTINUE)
- return rc;
+ ctxt->ops->get_fpu(ctxt);
+
+ if (ctxt->mode < X86EMUL_MODE_PROT64) {
+ rc = asm_safe("fxsave %[fx]", , [fx] "+m"(fx_state));
+ if (rc != X86EMUL_CONTINUE)
+ return rc;
+ /*
+ * Hardware doesn't save and restore XMM 0-7 without
+ * CR4.OSFXSR, but does save and restore MXCSR.
+ */
+ if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_OSFXSR)
+ size = offsetof(struct fxregs_state, xmm_space[8]);
+ else
+ size = offsetof(struct fxregs_state, xmm_space[0]);
+ rc = segmented_read_std(ctxt, ctxt->memop.addr.mem, &fx_state,
+ size);
+ if (rc != X86EMUL_CONTINUE)
+ return rc;
+ } else if (ctxt->mode == X86EMUL_MODE_PROT64) {
+ size = offsetof(struct fxregs_state, xmm_space[16]);
+ rc = segmented_read_std(ctxt, ctxt->memop.addr.mem, &fx_state,
+ size);
+ if (rc != X86EMUL_CONTINUE)
+ return rc;
+ }
if (fx_state.mxcsr >> 16)
return emulate_gp(ctxt, 0);
- ctxt->ops->get_fpu(ctxt);
-
- if (ctxt->mode < X86EMUL_MODE_PROT64)
- rc = fxrstor_fixup(ctxt, &fx_state);
-
if (rc == X86EMUL_CONTINUE)
rc = asm_safe("fxrstor %[fx]", : [fx] "m"(fx_state));
--
2.11.0
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Re: [PATCH] KVM: x86: dynamically allocate large struct in em_fxrstor Nick Desaulniers <nick.desaulniers@gmail.com> - 2017-05-25 03:40 +0200
Re: [PATCH] KVM: x86: dynamically allocate large struct in em_fxrstor Paolo Bonzini <pbonzini@redhat.com> - 2017-05-25 16:10 +0200
Re: [PATCH] KVM: x86: dynamically allocate large struct in em_fxrstor Nick Desaulniers <nick.desaulniers@gmail.com> - 2017-05-26 06:20 +0200
Re: [PATCH] KVM: x86: dynamically allocate large struct in em_fxrstor Paolo Bonzini <pbonzini@redhat.com> - 2017-05-26 09:20 +0200
[PATCH v2] KVM: x86: avoid large stack allocations in em_fxrstor Nick Desaulniers <nick.desaulniers@gmail.com> - 2017-05-29 22:00 +0200
Re: [PATCH v2] KVM: x86: avoid large stack allocations in em_fxrstor Nick Desaulniers <nick.desaulniers@gmail.com> - 2017-05-29 22:30 +0200
[PATCH v3] KVM: x86: avoid large stack allocations in em_fxrstor Nick Desaulniers <nick.desaulniers@gmail.com> - 2017-05-29 22:40 +0200
[PATCH v4] KVM: x86: avoid large stack allocations in em_fxrstor Nick Desaulniers <nick.desaulniers@gmail.com> - 2017-05-30 00:50 +0200
Re: [PATCH v4] KVM: x86: avoid large stack allocations in em_fxrstor Paolo Bonzini <pbonzini@redhat.com> - 2017-05-30 12:20 +0200
Re: [PATCH v4] KVM: x86: avoid large stack allocations in em_fxrstor Radim Krčmář <rkrcmar@redhat.com> - 2017-05-30 16:10 +0200
[PATCH v5] KVM: x86: avoid large stack allocations in em_fxrstor Nick Desaulniers <nick.desaulniers@gmail.com> - 2017-05-31 05:10 +0200
Re: [PATCH v5] KVM: x86: avoid large stack allocations in em_fxrstor Paolo Bonzini <pbonzini@redhat.com> - 2017-05-31 13:10 +0200
Re: [PATCH v5] KVM: x86: avoid large stack allocations in em_fxrstor Nick Desaulniers <nick.desaulniers@gmail.com> - 2017-06-01 03:10 +0200
Re: [PATCH v5] KVM: x86: avoid large stack allocations in em_fxrstor Paolo Bonzini <pbonzini@redhat.com> - 2017-06-01 09:40 +0200
Re: [PATCH v5] KVM: x86: avoid large stack allocations in em_fxrstor Nick Desaulniers <nick.desaulniers@gmail.com> - 2017-06-02 04:20 +0200
Re: [PATCH v3] KVM: x86: avoid large stack allocations in em_fxrstor Nick Desaulniers <nick.desaulniers@gmail.com> - 2017-05-30 00:50 +0200
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