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x86/speculation: Add virtualized speculative store bypass disable support

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Some AMD processors only support a non-architectural means of enabling
speculative store bypass disable (SSBD).  To allow a simplified view of
this to a guest, an architectural definition has been created through a new
CPUID bit, 0x80000008_EBX[25], and a new MSR, 0xc001011f.  With this, a
hypervisor can virtualize the existence of this definition and provide an
architectural method for using SSBD to a guest.

Add the new CPUID feature, the new MSR and update the existing SSBD
support to use this MSR when present.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
This commit is contained in:
Tom Lendacky 2018-05-17 17:09:18 +02:00 • committed by Thomas Gleixner
parent ccbcd26744
commit 11fb068349
4 changed files with 18 additions and 2 deletions
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13
arch/x86/kernel/process.c
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@ -388,6 +388,15 @@ static __always_inline void amd_set_core_ssb_state(unsigned long tifn)
}
#endif
static __always_inline void amd_set_ssb_virt_state(unsigned long tifn)
{
/*
* SSBD has the same definition in SPEC_CTRL and VIRT_SPEC_CTRL,
* so ssbd_tif_to_spec_ctrl() just works.
*/
wrmsrl(MSR_AMD64_VIRT_SPEC_CTRL, ssbd_tif_to_spec_ctrl(tifn));
}
static __always_inline void intel_set_ssb_state(unsigned long tifn)
{
u64 msr = x86_spec_ctrl_base | ssbd_tif_to_spec_ctrl(tifn);
@ -397,7 +406,9 @@ static __always_inline void intel_set_ssb_state(unsigned long tifn)
static __always_inline void __speculative_store_bypass_update(unsigned long tifn)
{
if (static_cpu_has(X86_FEATURE_LS_CFG_SSBD))
if (static_cpu_has(X86_FEATURE_VIRT_SSBD))
amd_set_ssb_virt_state(tifn);
else if (static_cpu_has(X86_FEATURE_LS_CFG_SSBD))
amd_set_core_ssb_state(tifn);
else
intel_set_ssb_state(tifn);