Messages in this thread Patch in this message | | | From | Ashwin Dayanand Kamat <> | Subject | [PATCH] x86/sev: Update ghcb_version only once | Date | Mon, 6 Nov 2023 12:02:41 +0530 |
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kernel crash was observed because of page fault, while running cpuhotplug ltp testcases on SEV-ES enabled systems. The crash was observed during hotplug after the CPU was offlined and the process was migrated to different cpu. setup_ghcb() is called again which tries to update ghcb_version in sev_es_negotiate_protocol(). Ideally this is a read_only variable which is initialised during booting. This results in pagefault.
From logs, [ 256.447466] BUG: unable to handle page fault for address: ffffffffba556e70 [ 256.447476] #PF: supervisor write access in kernel mode [ 256.447478] #PF: error_code(0x0003) - permissions violation [ 256.447479] PGD 8000667c0f067 P4D 8000667c0f067 PUD 8000667c10063 PMD 80080006674001e1 [ 256.447483] Oops: 0003 [#1] PREEMPT SMP NOPTI [ 256.447487] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.1.45-8.ph5 #1-photon . . . . . [ 256.447511] CR2: ffffffffba556e70 CR3: 0008000667c0a004 CR4: 0000000000770ee0 [ 256.447514] PKRU: 55555554 [ 256.447515] Call Trace: [ 256.447516] <TASK> [ 256.447519] ? __die_body.cold+0x1a/0x1f [ 256.447526] ? __die+0x2a/0x35 [ 256.447528] ? page_fault_oops+0x10c/0x270 [ 256.447531] ? setup_ghcb+0x71/0x100 [ 256.447533] ? __x86_return_thunk+0x5/0x6 [ 256.447537] ? search_exception_tables+0x60/0x70 [ 256.447541] ? __x86_return_thunk+0x5/0x6 [ 256.447543] ? fixup_exception+0x27/0x320 [ 256.447546] ? kernelmode_fixup_or_oops+0xa2/0x120 [ 256.447549] ? __bad_area_nosemaphore+0x16a/0x1b0 [ 256.447551] ? kernel_exc_vmm_communication+0x60/0xb0 [ 256.447556] ? bad_area_nosemaphore+0x16/0x20 [ 256.447558] ? do_kern_addr_fault+0x7a/0x90 [ 256.447560] ? exc_page_fault+0xbd/0x160 [ 256.447563] ? asm_exc_page_fault+0x27/0x30 [ 256.447570] ? setup_ghcb+0x71/0x100 [ 256.447572] ? setup_ghcb+0xe/0x100 [ 256.447574] cpu_init_exception_handling+0x1b9/0x1f0
Fix is to avoid updating the variable after it has been initialised during booting.
Fixes: 95d33bfaa3e1 ("x86/sev: Register GHCB memory when SEV-SNP is active") Signed-off-by: Ashwin Dayanand Kamat <kashwindayan@vmware.com> Co-developed-by: Bo Gan <ganb@vmware.com> --- arch/x86/kernel/sev-shared.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c index ccb0915e84e1..a447908f2b4d 100644 --- a/arch/x86/kernel/sev-shared.c +++ b/arch/x86/kernel/sev-shared.c @@ -144,6 +144,9 @@ static bool sev_es_negotiate_protocol(void) { u64 val; + if (ghcb_version) + return true; + /* Do the GHCB protocol version negotiation */ sev_es_wr_ghcb_msr(GHCB_MSR_SEV_INFO_REQ); VMGEXIT(); -- 2.39.0
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