RE: [PATCH AUTOSEL 5.5 389/542] clocksource/drivers/hyper-v: Reserve PAGE_SIZE space for tsc page
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From: Michael Kelley <hidden>
Date: 2020-02-14 17:18:33
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lkml, stable
This patch does not need to be backported to any stable releases. It is prep work for guests on Hyper-V ARM64 when the guest page size is 16K or 64K, and that functionality isn't upstream yet. Michael
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-----Original Message----- From: Sasha Levin <sashal@kernel.org> Sent: Friday, February 14, 2020 7:46 AM To: linux-kernel@vger.kernel.org; stable@vger.kernel.org Cc: Boqun Feng <redacted>; linux-hyperv@vger.kernel.org; Michael Kelley [off-list ref]; Daniel Lezcano [off-list ref]; Sasha Levin [off-list ref] Subject: [PATCH AUTOSEL 5.5 389/542] clocksource/drivers/hyper-v: Reserve PAGE_SIZE space for tsc page From: Boqun Feng <redacted> [ Upstream commit ddc61bbc45017726a2b450350d476b4dc5ae25ce ] Currently, the reserved size for a tsc page is 4K, which is enough for communicating with hypervisor. However, in the case where we want to export the tsc page to userspace (e.g. for vDSO to read the clocksource), the tsc page should be at least PAGE_SIZE, otherwise, when PAGE_SIZE is larger than 4K, extra kernel data will be mapped into userspace, which means leaking kernel information. Therefore reserve PAGE_SIZE space for tsc_pg as a preparation for the vDSO support of ARM64 in the future. Also, while at it, replace all reference to tsc_pg with hv_get_tsc_page() since it should be the only interface to access tsc page. Signed-off-by: Boqun Feng (Microsoft) <redacted> Cc: linux-hyperv@vger.kernel.org Reviewed-by: Michael Kelley <redacted> Signed-off-by: Daniel Lezcano <redacted> Link: https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fr %2F20191126021723.4710-1- boqun.feng%40gmail.com&data=02%7C01%7Cmikelley%40microsoft.com%7C2f481a9 3db624cb4b5e208d7b16691f6%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C6371 72926408924092&sdata=%2F1JNMBiq7l1ufSsWphZb%2FMLNep2EIOCzlXcG%2F9foZNw %3D&reserved=0 Signed-off-by: Sasha Levin <sashal@kernel.org> --- drivers/clocksource/hyperv_timer.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c index 287d8d58c21ac..b6ea3a2093c56 100644 --- a/drivers/clocksource/hyperv_timer.c +++ b/drivers/clocksource/hyperv_timer.c@@ -307,17 +307,20 @@ EXPORT_SYMBOL_GPL(hv_stimer_global_cleanup); struct clocksource *hyperv_cs; EXPORT_SYMBOL_GPL(hyperv_cs); -static struct ms_hyperv_tsc_page tsc_pg __aligned(PAGE_SIZE); +static union { + struct ms_hyperv_tsc_page page; + u8 reserved[PAGE_SIZE]; +} tsc_pg __aligned(PAGE_SIZE); struct ms_hyperv_tsc_page *hv_get_tsc_page(void) { - return &tsc_pg; + return &tsc_pg.page; } EXPORT_SYMBOL_GPL(hv_get_tsc_page); static u64 notrace read_hv_clock_tsc(struct clocksource *arg) { - u64 current_tick = hv_read_tsc_page(&tsc_pg); + u64 current_tick = hv_read_tsc_page(hv_get_tsc_page()); if (current_tick == U64_MAX) hv_get_time_ref_count(current_tick);@@ -372,7 +375,7 @@ static bool __init hv_init_tsc_clocksource(void) return false; hyperv_cs = &hyperv_cs_tsc; - phys_addr = virt_to_phys(&tsc_pg); + phys_addr = virt_to_phys(hv_get_tsc_page()); /* * The Hyper-V TLFS specifies to preserve the value of reserved --2.20.1